Methods for the compensation of imaging technique in the processing of radiographic images

ABSTRACT

The present invention relates to methods and devices for analyzing x-ray images. In particular, devices, methods and algorithms are provided that allow for the accurate and reliable evaluation of bone structure and macro-anatomical parameters from x-ray images.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/809,578 filed onMar. 25, 2004, which in turn claims the benefit of U.S. ProvisionalApplication Nos. 60/457,599, filed Mar. 25, 2003, and 60/478,454, filedJun. 13, 2003, and the disclosures of all of the foregoing applicationsare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention is in the field of imaging and analysis thereof.In particular, methods and compositions for accurately analyzing imagesto determine bone mineral density and/or bone structure are described.

BACKGROUND OF THE INVENTION

Osteoporosis is a condition that affects millions of Americans.Osteoporosis refers to a condition characterized by low bone mass andmicroarchitectural deterioration of bone tissue, with a consequentincrease of bone fragility and susceptibility to fracture. Osteoporosispresents commonly with vertebral fractures or hip fractures due to thedecrease in bone mineral density and deterioration of structuralproperties and microarchitecture of bone.

Imaging techniques are important diagnostic tools, particularly for bonerelated conditions. Currently available techniques for the noninvasiveassessment of the skeleton for the diagnosis of osteoporosis or theevaluation of an increased risk of fracture include dual x-rayabsorptiometry (DXA) (Eastell et al. (1998) New Engl J. Med338:736-746); quantitative computed tomography (QCT) (Cann (1988)Radiology 166:509-522); peripheral DXA (pDXA) (Patel et al. (1999) JClin Densitom 2:397-401); peripheral QCT (pQCT) (Gluer et. al. (1997)Semin Nucl Med 27:229-247); x-ray image absorptiometry (RA) (Gluer et.al. (1997) Semin Nucl Med 27:229-247); and quantitative ultrasound (QUS)(Njeh et al. “Quantitative Ultrasound: Assessment of Osteoporosis andBone Status” 1999, Martin-Dunitz, London England; U.S. Pat. No.6,077,224, incorporated herein by reference in its entirety). (See,also, WO 9945845; WO 99/08597; and U.S. Pat. No. 6,246,745).

DXA of the spine and hip has established itself as the most widely usedmethod of measuring BMD. Tothill, P. and D. W. Pye, (1992) Br J Radiol65:807-813. The fundamental principle behind DXA is the measurement ofthe transmission through the body of x-rays of 2 different photon energylevels. Because of the dependence of the attenuation coefficient on theatomic number and photon energy, measurement of the transmission factorsat 2 energy levels enables the area densities (i.e., the mass per unitprojected area) of 2 different types of tissue to be inferred. In DXAscans, these are taken to be bone mineral (hydroxyapatite) and softtissue, respectively. However, it is widely recognized that the accuracyof DXA scans is limited by the variable composition of soft tissue.Because of its higher hydrogen content, the attenuation coefficient offat is different from that of lean tissue. Differences in the softtissue composition in the path of the x-ray beam through bone comparedwith the adjacent soft tissue reference area cause errors in the BMDmeasurements, according to the results of several studies. Tothill, P.and D. W. Pye, (1992) Br J Radiol, 65:807-813; Svendsen, O. L., et al.,(1995) J Bone Min Res 10:868-873. Moreover, DXA systems are large andexpensive, ranging in price between $75,000 and $150,000.

Quantitative computed tomography (QCT) is usually applied to measure thetrabecular bone in the vertebral bodies. Cann (1988) Radiology166:509-522. QCT studies are generally performed using a single kVsetting (single-energy QCT), when the principal source of error is thevariable composition of the bone marrow. However, a dual-kV scan(dual-energy QCT) is also possible. This reduces the accuracy errors butat the price of poorer precision and higher radiation dose. Like DXA,however, QCT are very expensive and the use of such equipment iscurrently limited to few research centers.

Quantitative ultrasound (QUS) is a technique for measuring theperipheral skeleton. Njeh et al. (1997) Osteoporosis Int 7:7-22; Njeh etal. Quantitative Ultrasound: Assessment of Osteoporosis and Bone Status.1999, London, England: Martin Dunitz. There is a wide variety ofequipment available, with most devices using the heel as the measurementsite. A sonographic pulse passing through bone is strongly attenuated asthe signal is scattered and absorbed by trabeculae. Attenuationincreases linearly with frequency, and the slope of the relationship isreferred to as broadband ultrasonic attenuation (BUA; units: dB/MHz).BUA is reduced in patients with osteoporosis because there are fewertrabeculae in the calcaneus to attenuate the signal. In addition to BUA,most QUS systems also measure the speed of sound (SOS) in the heel bydividing the distance between the sonographic transducers by thepropagation time (units: m/s). SOS values are reduced in patients withosteoporosis because with the loss of mineralized bone, the elasticmodulus of the bone is decreased. There remain, however, severallimitations to QUS measurements. The success of QUS in predictingfracture risk in younger patients remains uncertain. Another difficultywith QUS measurements is that they are not readily encompassed withinthe WHO definitions of osteoporosis and osteopenia. Moreover, nointervention thresholds have been developed. Thus, measurements cannotbe used for therapeutic decision-making.

There are also several technical limitations to QUS. Many devices use afoot support that positions the patient's heel between fixedtransducers. Thus, the measurement site is not readily adapted todifferent sizes and shapes of the calcaneus, and the exact anatomic siteof the measurement varies from patient to patient. It is generallyagreed that the relatively poor precision of QUS measurements makes mostdevices unsuitable for monitoring patients' response to treatment. Gluer(1997) J Bone Min Res 12:1280-1288.

Radiographic absorptiometry (RA) is a technique that was developed manyyears ago for assessing bone density in the hand, but the technique hasrecently attracted renewed interest. Gluer et al. (1997) Semin Nucl Med27:229-247. With this technique, BMD is measured in the phalanges. Theprincipal disadvantage of RA of the hand is the relative lack of highturnover trabecular bone. For this reason, RA of the hand has limitedsensitivity in detecting osteoporosis and is not very useful formonitoring therapy-induced changes.

Peripheral x-ray absorptiometry methods such as those described aboveare substantially cheaper than DXA and QCT with system prices rangingbetween $15,000 and $35,000. However, epidemiologic studies have shownthat the discriminatory ability of peripheral BMD measurements topredict spine and hip fractures is lower than when spine and hip BMDmeasurements are used. Cummings et al. (1993) Lancet 341:72-75; Marshallet al. (1996) Br Med J 312:1254-1259. The main reason for this is thelack of trabecular bone at the measurement sites used with thesetechniques. In addition, changes in forearm or hand BMD in response tohormone replacement therapy, bisphosphonates, and selective estrogenreceptor modulators are relatively small, making such measurements lesssuitable than measurements of principally trabecular bone for monitoringresponse to treatment. Faulkner (1998) J Clin Densitom 1:279-285;Hoskings et al. (1998) N Engl J Med 338:485-492. Although attempts toobtain information on bone mineral density from dental x-rays have beenattempted (See, e.g., Shrout et al. (2000) J. Periodonol. 71:335-340;Verhoeven et al. (1998) Clin Oral Implants Res 9(5):333-342), these havenot provided accurate and reliable results.

Furthermore, current methods and devices do not generally take intoaccount bone structure analyses. See, e.g., Ruttimann et al. (1992) OralSurg Oral Med Oral Pathol 74:98-110; Southard & Southard (1992) OralSurg Oral Med Oral Pathol 73:751-9; White & Rudolph, (1999) Oral SurgOral Med Oral Pathol Oral Radiol Endod 88:628-35.

Thus, although a number of devices and methods exist for evaluatingbone, there are a number of limitations on such devices and methods.Consequently, the inventors have recognized the need, among otherthings, to provide methods and compositions that result in the abilityto obtain accurate bone mineral density and bone structure informationfrom images (e.g., radiographic images) and data.

SUMMARY OF THE INVENTION

In one aspect, the disclosure provides a method to derive informationregarding one or more bone parameters from an image, the methodcomprising the steps of: (a) obtaining an image comprising bone from asubject; (b) defining two or more regions of interest (ROIs) in theimage; and (c) analyzing a plurality of positions in the ROIs todetermine one or more parameters selected from the group consisting ofbone microarchitecture, bone macro-anatomy, biomechanical parameters andcombinations thereof of the ROIs. In certain embodiments, the ROIs areoverlapping. The positions analyzed in the ROIs may be at regularintervals relative to one another or, alternatively, may be irregularlyspaced relative to each other. Thus, in certain embodiments, the methodsinvolve determining bone micro-architecture, for example by analyzingpositions at regular intervals. In other embodiments, the methodsinvolve determining bone macro-anatomy, for example by analyzingpositions at irregular intervals in the image.

In any of the methods described herein, the image can be two-dimensional(2D) or three-dimensional (3D). The images may be x-rays, MRI images,CAT scan images, or any other image including bone. In any of themethods, the image may be an electronic image.

In any of the methods described herein, the subject can be, for example,an osteoporosis subject.

In another aspect, this disclosure relates to a method of generating amap of one or more bone parameters, the method comprising the steps of(a) obtaining information on bone parameters according to the method ofany of methods described herein; and (b) identifying regions of theimage that exhibit similar parameter characteristics, thereby creating aparameter map of the image.

In yet another aspect, a method of predicting a fracture path in asubject is provided, the method comprising the steps of: (a) generatingmultiple parameter maps according to any of the methods of generatingparameters maps described herein; (b) generating a composite parametermap from the multiple parameters maps of step (a); and (c) analyzing thecomposite parameter map to identify possible fracture paths.

In yet another aspect, the invention includes a method of predicting afracture path in a subject, the method comprising the steps of: (a)analyzing of one or more parameter maps preparing according to any ofthe methods described herein, wherein the analysis is watershedsegmentation analysis or Markov random field analysis; and (c)identifying possible fracture paths based on the analysis of step (a),thereby predicting a fracture path in the subject.

In another aspect, the invention includes a method of predicting therisk of fracture in a subject, the method comprising the steps of: (a)generating a finite element model from one or more parameter mapsobtained according any of the methods described herein; (b) applyingsimulated force vectors that would occur during a fracture incident tothe finite element model generated in step(s); and (c) determining theminimum forces required for fracture to occur, thereby estimating therisk of fracture.

In a still further aspect, the invention includes a method ofdetermining the risk of fracture in a subject comprising: (a) predictinga fracture path according to any of the methods of predicting fracturepath as described herein; (b) evaluating one or more selected boneparameters along the predicted fracture path, thereby estimating therisk of fracture.

In another aspect, the invention includes a method of treating a subjectwith bone disease comprising (a) obtaining an image from a subject; (b)analyzing the image obtained in step (a) using any of the methodsdescribed herein; (c) diagnosing a bone disease based on the analysis ofstep (b); and (d) selecting and administering a suitable treatment tosaid subject based on said diagnosis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a dental x-ray. A calibration phantom 110 isseen. Regions of interest 120 have been placed for measurement of bonemineral density or structure.

FIG. 2 shows another example of a dental x-ray. A calibration phantom110 is seen. Regions of interest 120 have been placed for measurement ofbone mineral density or structure.

FIG. 3 shows an example of an analysis report resulting from ameasurement of mandibular or maxillary bone mineral density. A subject(X) is more than one standard deviation below the mean of age-matchedcontrols (x-axis age, y-axis arbitrary units BMD).

FIG. 4 shows an example of a V-shaped calibration phantom 110 mounted ona tooth 120. Gums are also shown 130.

FIG. 5 shows an example of a holder 115 for a calibration phantom 110.The holder 115 is mounted on a tooth 120. Gums are also shown 130.

FIG. 6, panels B through E shows gray value profiles along differentrows of pixels used for locating dental apices. From top to bottom, thecharacteristic peaks for the dental roots (shown in dental x-ray panelA) gradually disappear.

FIG. 7 shows a Hough transform (panel A) of a test image (panel B). Allcollinear points from the same line are transformed into sinusoidalcurves that intersect in a single point (circles).

FIG. 8 shows a Hough transform (panel A) of a skeletonized trabecularbone x-ray image (panel B). The white regions in panel A indicate longersegments and predominant angles.

FIG. 9 shows the effect of varying size of structuring element E₂;calibration phantom image with lines of varying width (1, 3, 5, 7, 9,11, 13 pix) (top left); skeleton operation performed using E₂ with adiameter of 3 pix (top right), 7 pix (bottom left), and 11 pix (bottomright), respectively.

FIG. 10 shows the effect of varying size of structuring element E₂; grayscale image of trabecular bone (top left, panel A); skeleton operationperformed using E₂ with a diameter of 3 pix (top right, panel B); 7 pix(bottom left, panel C) and 11 pix (bottom right, panel D), respectively.

FIG. 11 shows gray value surface plot of an anatomical region ofinterest from a dental x-ray (inset) used for fractal analysis.

FIG. 12 shows an example of a hygienic cover holder that includescompartments for a calibration phantom and a fluid-filled bolus back.

FIG. 13 shows an example of an anatomical region of interest (blackdot), determined relative to the teeth or to the convexity/concavity ofthe mandible.

FIG. 14 shows an example of three anatomical region of interests (blackdots), determined relative to the teeth or to the convexity/concavity ofthe mandible.

FIG. 15 is a side view of an exemplary system for minimizing tubeangulation as described herein. In the Figure, the system is shown as adental x-ray system. An extension tubing (200) is attached to aring-shaped Rinn holder (102). The outer diameter of the extensiontubing is slightly smaller than the inner diameter of the tube locatedin front of the dental x-ray system/dental x-ray tube. The extensiontubing can then be inserted into the metal tube thereby reducing tubeangulation and resultant errors in bone apparent density and bonestructural measurements.

FIG. 16 depicts an example of a regular interval sampling field formicroarchitecture (+) and a higher density sampling field formacro-anatomical features (*) on a femur radiograph. White rectanglesare examples of overlapping window positioning.

FIG. 17 depicts watershed segmentation boundaries superimposed on aparameter map. The two white lines are the actual fracture pathsresulted from an in-vitro mechanical loading test.

FIG. 18 is a flowchart depicting an exemplary process to determinefracture risk using overlapping window processing and fracture pathsprediction.

FIG. 19 depicts a Markov random field analysis by modeling particularjoint feature distributions as they are estimated at each image elementor image neighborhood.

FIG. 20 depicts an exemplary model definition for trabecular patterndensity characterization in a region of interest (ROI) with a noisemodel P(N) and characteristic structure pattern given a density levelP(I|Ti).

FIG. 21 depicts exemplary Bayes' Rule analysis.

FIG. 22 depicts an example of a regular interval sampling field formicroarchitecture (+) and a higher density sampling field formacro-anatomical features (*) on a spine radiograph. White rectanglesare examples of overlapping window positioning.

FIG. 23 depicts an example of a sampling field of varying density formicroarchitecture (+, x, diamond) and a regular sampling field formacro-anatomical features (*) on a knee radiograph. White rectangles areexamples of overlapping window positioning.

FIG. 24 depicts an example of an application of structure extraction andmeasurement for therapeutic monitoring using spine x-ray. White outlineof extracted structure are show in (a) before treatment, and (b) aftertreatment.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable any person skilled inthe art to make and use the invention. Various modifications to theembodiments described will be readily apparent to those skilled in theart, and the generic principles defined herein can be applied to otherembodiments and applications without departing from the spirit and scopeof the present invention. Thus, the present invention is not intended tobe limited to the embodiments shown, but is to be accorded the widestscope consistent with the principles and features disclosed and shownherein. To the extent necessary to achieve a complete understanding ofthe invention disclosed, the specification and drawings of all issuedpatents, patent publications, and patent applications cited in thisapplication are incorporated herein by reference.

The practice of the present invention employs, unless otherwiseindicated, conventional methods of imaging and image processing withinthe skill of the art. Such techniques are explained fully in theliterature. See, e.g., WO 02/22014, incorporated herein in its entiretyby reference; X-Ray Structure Determination: A Practical Guide, 2ndEdition, editors Stout and Jensen, 1989, John Wiley & Sons, publisher;Body CT: A Practical Approach, editor Slone, 1999, McGraw-Hillpublisher; The Essential Physics of Medical Imaging, editors Bushberg,Seibert, Leidholdt Jr & Boone, 2002, Lippincott, Williams & Wilkins;X-ray Diagnosis: A Physician's Approach, editor Lam, 1998Springer-Verlag, publisher; and Dental Radiology: Understanding theX-Ray Image, editor Laetitia Brocklebank 1997, Oxford University Presspublisher.

Methods and compositions useful in analyzing images are described. Inparticular, the invention includes methods of obtaining and/or derivinginformation about bone mineral density and/or bone structure from animage. Additionally, the present invention relates to the provision ofaccurate calibration phantoms for use in determining bone structure andmethods of using these calibration phantoms. In particular, the presentinvention recognizes for the first time that errors arising frommisplacement of interrogation sites in dental or hip x-rays of bonedensity and/or bone structure can be corrected by positioning the x-raytube, the detector and/or the calibration reference with respect to ananatomical landmark (or anatomical region of interest).

Advantages of the present invention include, but are not limited to, (i)providing accessible and reliable means for analyzing x-rays; (ii)providing non-invasive measurements of bone structure and architectureand macro-anatomy; (iii) providing methods of diagnosing bone conditions(e.g., osteoporosis, fracture risk); (iv) providing methods of treatingbone conditions; and (iv) providing these methods in cost-effectivemanner.

1.0. Obtaining Data from Images

An image can be acquired using well-known techniques from any localsite. Non-limiting examples of imaging techniques suitable for acquiringimages from which data can be obtained include, ultrasound, CAT scan,MRI and the like. See, also, “Primer of Diagnostic Imaging,” 3rdedition, eds. Weissleder et al. (2002), Mosby Press; and InternationalPublication WO 02/22014.

In certain aspects, 2D planar x-ray imaging techniques are used. 2Dplanar x-ray imaging is a method that generates an image by transmittingan x-ray beam through a body or structure or material and by measuringthe x-ray attenuation on the other side of said body or said structureor said material. 2D planar x-ray imaging is distinguishable fromcross-sectional imaging techniques such as computed tomography ormagnetic resonance imaging. If the x-ray image was captured usingconventional x-ray film, the x-ray can be digitized using any suitablescanning device. Digitized x-ray images can be transmitted over anetworked system, e.g. the Internet, into a remote computer or server.It will be readily apparent that x-ray images can also be acquired usingdigital acquisition techniques, e.g. using photostimulable phosphordetector systems or selenium or silicon detector systems, the x-rayimage information is already available in digital format which can beeasily transmitted over a network. In other embodiments, 3D images areacquired, for example, using 3D imaging techniques and/or by creating 3Dimages from 2D images.

Any images can be used including, but not limited to, digital x-rays andconventional x-ray film (which can be digitized using commerciallyavailable flatbed scanners). In certain embodiments, the x-ray is of thehip region, for example performed using standard digital x-ray equipment(Kodak DirectView DR 9000, Kodak, Rochester, N.Y.). Patients aretypically positioned on an x-ray table in supine position, parallel tothe long axis of the table, with their arms alongside their body. Thesubject's feet may be placed in neutral position with the toes pointingup or in internal rotation or may be placed in a foot holder such thatthe foot in a neutral position (0° rotation) or in any desired angle ofrotation (e.g., internal or external) relative to neutral (see, alsoExample 8 below). Foot holders suitable for such purposes may include,for example, a base plate extending from the foot, for example, from themid to distal thigh to the heel. The base plate preferably sits on thex-ray table. The patients' foot is positioned so that the posterioraspect of the heel is located on top of the base plate. The medialaspect of the foot is placed against a medial guide connected rigidly tothe base plate at a 90° angle by any suitable means (e.g., straps,velcro, plastic, tape, etc.). A second, lateral guide attached to thebase plate at a 90° angle with a sliding mechanism can then be movedtoward the lateral aspect of the foot and be locked in position, forexample when it touches the lateral aspect of the foot. The use of afoot holder can help improve the reproducibility of measurements of bonestructure parameters or macro-anatomical and/or biomechanicalparameters.

As will be appreciated by those of skill in the art, the patient orsubject can be any warm-blooded animal. Typically patients, or subjects,are chosen from the class Mammalia. Thus, for example, patients, orsubjects, would include humans and nonhuman primates such as chimpanzeesand other apes and monkey species; farm animals such as cattle, sheep,pigs, goats and horses; domestic mammals such as dogs and cats;laboratory animals including rodents such as mice, rats and guinea pigs,and the like. To the extent desirable, other non-mammals can besubjected to the protocols described herein without departing from thescope of the invention,

Persons of skill in the art will appreciate that macro-anatomicalparameters generally describe the shape, size or thickness of boneand/or surrounding structure. Oftentimes the typical parameters are, butneed not be, greater than 0.5 mm in size in at least one dimension.Generally, in the hip joint, macro-anatomical parameters includethickness of the femoral shaft cortex, thickness of the femoral neckcortex, cortical width, hip axis length, CCD (caput-collum-diaphysis)angle, neck-shaft angle and width of the trochanteric region. In thespine, macro-anatomical parameters include thickness of the superior andinferior endplate, thickness of the anterior, lateral and posteriorvertebral walls, diameter and height of the vertebral body, dimensionsof the spinal canal and the posterior elements.

Generally, the ray is centered onto the hip joint medial and superior tothe greater trochanter. A calibration phantom, such as an aluminum stepwedge may also be included in the images to calibrate gray values beforefurther image analysis.

In other embodiments, dental x-rays are preferred because of therelative ease and lack of expense in obtaining these images. Further,the mandible and maxilla are primarily composed of trabecular bone.Since the metabolic turnover of trabecular bone is approximately eighttimes greater than that of cortical bone, areas of predominantlytrabecular bone such as the vertebral body are preferred sites formeasuring bone mineral density. Lang et al. (1991) Radiol Clin North Am29:49-76. Thus, trabecular bone is clearly visible on the dental x-rayimage, thus facilitating quantitative analysis of bone mineral densityand structure. Jeffcoat et al. (2000) Periodontol 23:94-102; Southard etal. (2000) J Dent Res 79:964-969. Further, the earliest bone loss inosteoporosis patients occurs in areas of trabecular bone. Multipledental x-ray images are commonly made in most Americans throughout life.Indeed, there are approximately 750 million U.S. dental visits annuallyand 150 million of these patients result in more than 1 billion dentalx-rays taken each year. Thus, the ability to diagnose osteoporosis ondental x-rays would be extremely valuable since it would create theopportunity for low-cost mass screening of the population.

Preferably, x-ray imaging is performed using standard x-ray equipment,for instance standard dental x-ray equipment (e.g. General ElectricMedical Systems, Milwaukee, Wis.). X-rays of the incisor region andcanine region are acquired using a standard x-ray imaging technique with80 kVp and automatic exposure using a phototimer or using a manualtechnique with 10 mA tube current. X-ray images are acquired, forexample, on Kodak Ultraspeed film (Kodak, Rochester, N.Y.). X-ray imagesmay be digitized using a commercial flatbed scanner with transparencyoption (Acer ScanPremio ST). Similarly, other imaging techniques aretypically performed using standard equipment, for instance, MRI or CATequipment.

1.1. Calibration Phantoms

It is highly preferred that the images include accurate referencemarkers, for example calibration phantoms for assessing bone mineraldensity and/or bone structure and/or one or more macro-anatomical and/orbiomechanical parameters on any given image. Calibration references(also known as calibration phantoms) for use in imaging technologieshave been described. See, e.g., U.S. Pat. No. 5,493,601 and U.S. Pat.No. 5,235,628. U.S. Pat. No. 5,335,260 discloses a calibration phantomrepresentative of human tissue containing variable concentrations ofcalcium that serves as reference for quantifying calcium, bone mass andbone mineral density in x-ray and CT imaging systems. However, currentlyavailable calibration phantoms are not always accurate. Because bonemineral density accounts for considerably less than 100% of fracturerisk in osteoporosis (Ouyang et al. (1997) Calif Tissue Int, 60:139-147)some of the methods and devices described herein are designed to assessnot only bone mineral density but also bone structure and, in addition,macro-anatomical and/or biomechanical parameters. By assessing two ormore of these parameters, more accurate testing and screening can beprovided for conditions such as osteoporosis.

Thus, in certain aspects, the current invention provides for methods anddevices that allow accurate quantitative assessment of informationcontained in an x-ray such as density of an anatomic structure and/ormorphology of an anatomic structure. Any suitable calibration phantomcan be used, for example, one that comprises aluminum or otherradio-opaque materials. U.S. Pat. No. 5,335,260 describes othercalibration phantoms suitable for use in assessing bone mineral densityin images. Examples of other suitable calibration reference materialscan be fluid or fluid-like materials, for example, one or more chambersfilled with varying concentrations of calcium chloride or the like.

Numerous calibration phantoms (or reference calibrations) can be used inthe practice of the present invention. Typically, the system used tomonitor bone mineral density and/or bone structure and/or one or moremacro-anatomical and/or biomechanical parameters in a target organismcomprises an image (e.g., a dental or hip radiograph), which providesinformation on the subject; an assembly including a calibration phantom,which acts as a reference for the data in the image; and at least onedata processing system, which evaluates and processes the data from theimage and/or from the calibration phantom assembly.

It will be readily apparent that a calibration phantom can contain asingle, known density or structure reference. Furthermore, a gradient indensity can be achieved by varying the thickness or the geometry of thecalibration phantom along the path of the x-ray beam, for example, byusing a V-shape of the calibration phantom of varying thickness (FIG.4). The calibration phantom can also include angles. For example, thecalibration phantom can be “T”-shaped or “L”-shaped thereby includingone or more 90 degree angles.

The calibration phantom can contain several different areas of differentradio-opacity. For example, the calibration phantom can have a step-likedesign, whereby changes in local thickness of the wedge result indifferences in radio-opacity. Stepwedges using material of varyingthickness are frequently used in radiology for quality control testingof x-ray beam properties. By varying the thickness of the steps, theintensity and spectral content of the x-ray beam in the projection imagecan be varied. Stepwedges are commonly made of aluminum, copper andother convenient and homogeneous materials of known x-ray attenuationproperties. Stepwedge-like phantoms can also contain calcium phosphatepowder or calcium phosphate powder in molten paraffin.

Alternatively, continuous wedges may be used or the calibrationreference may be designed such that the change in radio-opacity is fromperiphery to center (for example in a round, ellipsoid, rectangular,triangular of other shaped structure). As noted above, the calibrationreference can also be constructed as plurality of separate chambers, forexample fluid filled chambers, each including a specific concentrationof a reference fluid (e.g., calcium chloride). In addition to one ormore fluids, a calibration phantom can also contain metal powder, e.g.aluminum or steel powder, embedded within it (for example, embedded in aplastic).

In certain embodiments, the calibration phantom is specifically designedto serve as a reference for bone structure (e.g., trabecular spacing,thickness and the like). For example, the calibration wedge can containone or more geometric patterns with known dimensions, e.g. a gridwhereby the spacing of a grid, thickness of individual grid elements,etc. are known. This known geometric pattern of radio-opaque elements inthe calibration phantom can be used to improve the accuracy ofmeasurements of trabecular bone structure in an x-ray. Such measurementsof trabecular bone structure can include, but are not limited to,trabecular spacing, trabecular length and trabecular thickness. Suchmeasurements of trabecular spacing, trabecular length and trabecularthickness can, for example, be performed in a dental or spine or hipx-ray. These calibration phantoms can be made up of a variety ofmaterials include, plastics, metals and combinations thereof. Further,the reference components can be solid, powdered, fluid or combinationsthereof. Thus, the calibration wedge can also be used to improvemeasurements of bone structure.

In certain embodiments, the calibration phantom is specifically designedto serve as a reference for macro-anatomical parameters (e.g., in thehip joint, thickness of the femoral shaft cortex, thickness of thefemoral neck cortex, cortical width, hip axis length, CCD(caput-collum-diaphysis) angle, neck-shaft angle and width of thetrochanteric region; and in the spine, thickness of the superior andinferior endplate, thickness of the anterior, lateral and posteriorvertebral walls, diameter and height of the vertebral body, dimensionsof the spinal canal and the posterior elements). For example, thecalibration wedge can contain one or more geometric patterns with knowndimensions, e.g. a grid whereby the spacing of a grid, thickness ofindividual grid elements, etc. are known. This known geometric patternof radio-opaque elements in the calibration phantom can be used toimprove the accuracy of measurements of macro-anatomical and/orbiomechanical parameters in an x-ray, for example by aiding in thecorrection of image magnification. Such measurements of macro-anatomicalparameters can, for example, be performed in a dental or spine or hipx-ray. These calibration phantoms can be made up of a variety ofmaterials include, plastics, metals and combinations thereof. Further,the reference components can be solid, powdered, fluid or combinationsthereof. Thus, the calibration wedge can also be used to improvemeasurements of bone structure.

Since the present invention contemplates analysis of dental x-ray imagesfor information on bone structure, bone mineral density or bothstructure and density, it will be apparent that calibration phantomswill be selected based on whether structure, density or both are beingmeasured. Thus, one or more calibration phantoms may be present.

Whatever the overall shape or composition of the calibration phantom,when present, the at least one marker be positioned at a known densityand/or structure in the phantom. Furthermore, it is preferred that atleast one geometric shape or pattern is included in the calibrationphantom. Any shape can be used including, but not limited to, squares,circles, ovals, rectangles, stars, crescents, multiple-sided objects(e.g., octagons), V- or U-shaped, inverted V- or U-shaped, irregularshapes or the like, so long as their position is known to correlate witha particular density of the calibration phantom. In preferredembodiments, the calibration phantoms described herein are used in 2Dplanar x-ray imaging.

The calibration phantoms can be imaged before or after the x-ray imageis taken. Alternatively, the calibration phantom can be imaged at thesame time as the x-ray image. The calibration phantom can be physicallyconnected to an x-ray film and/or film holder. Such physical connectioncan be achieved using any suitable mechanical or other attachmentmechanism, including but not limited to adhesive, a chemical bond, useof screws or nails, welding, a Velcro™ strap or Velcro™ material and thelike. Similarly, a calibration phantom can be physically connected to adetector system or a storage plate for digital x-ray imaging using oneor more attachment mechanisms (e.g., a mechanical connection device, aVelcro™ strap or other Velcro™ material, a chemical bond, use of screwsor nails, welding and an adhesive). The external standard and the filmcan be connected with use of a holding device, for example using pressfit for both film and external standard.

Additionally, the calibration phantom assembly can be attached to ananatomical structure, for example one or more teeth, mucus membranes,the mandible and/or maxilla. For instance, the calibration phantom canbe attached (e.g., via adhesive attachment means) to the epithelium ormucous membrane inside overlying the mandible or the maxilla.Alternatively, the calibration phantom can be placed on or adjacent to atooth, for example, a V- or U-shaped (in the case of the maxilla) or aninverted V- or U-shaped (in the case of the mandible) calibrationphantom can be used. The opening of the V or U will be in contact withthe free edge of at least one tooth or possibly several teeth (FIG. 4).

In preferred embodiments, when an x-ray of an anatomic structure or anon-living object is acquired a calibration phantom is included in thefield of view. Any suitable calibration phantom can be used, forexample, one that comprises aluminum or other radio-opaque materials.U.S. Pat. No. 5,335,260 describes other calibration phantoms suitablefor use in assessing bone mineral density in images. Examples of othersuitable calibration reference materials can be fluid or fluid-likematerials, for example, one or more chambers filled with varyingconcentrations of calcium chloride or the like. In a preferredembodiment, the material of the phantom is stainless steel (e.g., AISIgrade 316 comprising carbon (0.08%); manganese (2%); silicon (1%);phosphorus (0.045%); sulphur (0.03%); nickel (10-14%); chromium(16-18%); molybdenum (2-3%); plus iron to make up 100%). The relativepercentages of the components may be with respect to weight or volume.

It will be apparent that calibration phantoms suitable for attachment toan anatomical structure can have different shapes depending on the shapeof the anatomical structure (e.g., tooth or teeth) on which or adjacentto which it will be placed including, but not limited to, U-shaped,V-shaped, curved, flat or combinations thereof. For example, U-shaped(or inverted U-shaped) calibration phantoms can be positioned on top ofmolars while V-shaped (or inverted V-shaped) calibration phantoms can bepositioned on top of incisors. Further, it will be apparent that incertain instances (e.g., teeth on the mandible), the calibration phantomcan rest on top of the tooth just based on its gravity or it can beattached to the tooth (e.g., using adhesive). In the case of the teethon the maxilla, the calibration phantom will typically be attached tothe tooth, for example with use of an adhesive.

Any of these attachments may be permanent or temporary and thecalibration phantom can be integral (e.g., built-in) to the film, filmholder and/or detector system or can be attached or positionedpermanently or temporarily appropriately after the film and/or filmholder is produced. Thus, the calibration phantom can be designed forsingle-use (e.g., disposable) or for multiple uses with different x-rayimages. Thus, in certain embodiments, the calibration phantom isreusable and, additionally, can be sterilized between uses. Integrationof a calibration phantom can be achieved by including a material ofknown x-ray density between two of the physical layers of the x-rayfilm. Integration can also be achieved by including a material of knownx-ray density within one of the physical layers of the x-ray film.Additionally, the calibration phantom can be integrated into the filmcover. A calibration phantom or an external standard can also beintegrated into a detector system or a storage plate for digital x-rayimaging. For example, integration can be achieved by including amaterial of known x-ray density between two of the physical layers ofthe detector system or the storage plate. Integration can also beachieved by including a material of know x-ray density within one of thephysical layers of the detector system or the storage plate.

In certain embodiments, for example those embodiments in which thecalibration phantom is temporarily attached to a component of the x-rayassembly system (e.g., x-ray film holder, x-ray film, detector system orthe like), cross-hairs, lines or other markers may be placed on theapparatus as indicators for positioning of the calibration phantom.These indicators can help to ensure that the calibration phantom ispositioned such that it doesn't project on materials that will alter theapparent density in the resulting image.

Any of the calibration phantom-containing assemblies described hereincan be used in methods of analyzing and/or quantifying bone structureand/or one or more macro-anatomical and/or biomechanical parameters (orbone mineral density) in an x-ray image. The methods generally involvesimultaneously imaging or scanning the calibration phantom and anothermaterial (e.g., bone tissue from a subject) for the purpose ofquantifying the density of the imaged material (e.g., bone mass). In thecase of dental radiographs, the calibration phantom, the x-ray tube ordental x-ray film is typically positioned in a manner to ensureinclusion of the calibration phantom and a portion of the mandibleand/or maxilla on the dental x-ray image. Preferably, the calibrationphantom, the x-ray tube and the dental x-ray film are positioned so thatat least a portion of the section of the mandible or maxilla included onthe image will contain predominantly trabecular bone rather thancortical bone.

Thus, under the method of the present invention, the calibration phantomis preferably imaged or scanned simultaneously with the individualsubject, although the invention allows for non-simultaneous scanning ofthe phantom and the subject. Methods of scanning and imaging structuresby x-ray imaging technique are well known. By placing the calibrationphantom in the x-ray beam with the subject, reference calibrationsamples allow corrections and calibration of the absorption propertiesof bone. When the phantom is imaged or scanned simultaneously with eachsubject, the variation in x-ray beam energy and beam hardening arecorrected since the phantom and the subject both see the same x-ray beamspectrum. Each subject, having a different size, thickness,muscle-to-fat ratio, and bone content, attenuate the beam differentlyand thus change the effective x-ray beam spectrum. It is necessary thatthe bone-equivalent calibration phantom be present in the same beamspectrum as the subject's bone to allow accurate calibration.

X-ray imaging assemblies that are currently in use do not take intoaccount the position of the calibration phantom in relation to thestructures being imaged. Thus, when included in known assemblies,calibration phantom(s) are often positioned such that they project onmaterials or structures (e.g., bone) that alter apparent density of thecalibration phantom in the resulting x-ray image. Clearly, thisalteration in apparent density will affect the accuracy of thecalibration phantom as a reference for determining bone mineral density,structure or macro-anatomical parameters. Therefore, it is an object ofthe invention to provide methods in which the calibration phantomprojects free of materials or structures that will alter the apparentdensity of the reference. In the context of dental x-rays, for instance,the methods described herein ensure that the calibration phantomprojects free of bone (e.g., teeth, jaw) tissue. This can beaccomplished in a variety of ways, for example, positioning thecalibration phantom in the x-ray film or in the x-ray film holder suchthat it will appear between the teeth in the dental x-ray.

The calibration phantom materials and methods of the present inventionare preferably configured to be small enough and thin enough to beplaced inside the mouth, and the method of the present invention can beused to quantify bone mass using standard dental x-ray systems, forexample by including temporary or permanent calibration phantoms indental x-ray film holders. Further, it is highly desirable that thecalibration phantom be positioned so that at least a portion doesn'tproject on structures or materials that will alter the apparent densityor structural characteristics of the calibration phantoms. It is alsopreferable to position calibration phantom at a defined distancerelative to at least one tooth or the mandible or the maxilla whereby asubstantial portion of the calibration phantom projects free of saidtooth, said mandible or said maxilla on the x-ray image. Any suitabledistance can be used, for example between about 1 mm and 5 cm or anyvalue therebetween.

A cross-calibration phantom can be used to optimize system performance,e.g. x-ray tube settings or film processor settings, or to improve thecomparability of different machines or systems, typically located atdifferent sites. For this purpose, a separate image may be obtainedwhich does not include a patient or a body part. The image includes theprimary calibration phantom used in patients, e.g. a step-wedge of knowndensity, and the cross-calibration phantom. The apparent density of theprimary calibration phantom is then calibrated against the density ofthe cross-calibration phantom. The resultant cross-calibration of theprimary phantom can help to improve the accuracy of measurements of bonedensity, bone structure and macro-anatomical and/or biomechanicalparameters. It can also help improve the overall reproducibility of themeasurements. In one embodiment of the invention, an x-ray technologistor a dental hygienist will perform a cross-calibration test once a day,typically early in the morning, prior to the first patient scans. Theresults of the cross-calibration or the entire cross-calibration studycan be transmitted via a network to a central computer. The centralcomputer can then perform adjustments designed to maintain a high levelof comparability between different systems.

1.2. Inherent Reference Markers

In certain embodiments of the invention, information inherent in theanatomic structure or the non-living object can be used to estimate thedensity and/or structure and/or macro-anatomy of selected bone regionsof interest within the anatomic structure or the non-living object. Forexample, since the density of muscle, fat, water (e.g., soft tissue),metal (e.g., dental fillings) and air are typically known, the densityof air surrounding an anatomic structure or non-living object, thedensity of subcutaneous fat, and the density of muscle tissue can beused to estimate the density of a selected region of bone, for examplewithin the distal radius. For instance, a weighted mean can bedetermined between one or more of the internal standards (e.g., air,water, metal, and/or fat) and used as internal standards to determinebone density in the same x-ray image. Similarly, the density of a toothor a portion of a tooth can be used to estimate the density of aselected region of bone, e.g. an area in the mandible.

The information inherent in said anatomic structure can also be combinedwith information provided by the calibration phantom and the combinationcan result in an improved accuracy of the calibration phantom.

1.3. Holders and Hygienic Covers

As noted above, in certain embodiments, a holder can be used to positionthe calibration phantom. The holder can be U-shaped or V-shaped (FIG. 5)for ease in attachment to a tooth. The attachment can be, for example,with an adhesive. The calibration phantom, in turn, can be attached tothe holder. Similarly, the calibration phantom can be attached toholders comprising one or more molds of at least one or more teeth.Additionally, the holder can be used to position both the film and thecalibration phantom relative to the osseous structure that will beincluded in the x-ray image. In another embodiment, a holding devicethat can hold the x-ray film is integrated in the calibration phantom.This holding device can hold the film in place prior to taking thex-ray. The holding device can be spring-loaded or use other means suchas mechanical means of holding and stabilizing the x-ray film.

In certain embodiments, the holder may comprise a disposable orsterilizable hygienic cover. See, e.g., WO 99/08598, the disclosure ofwhich is incorporated by reference herein in its entirety. Furthermore,the holder may comprise multiple components, for example, thecalibration phantom and a integrated or insertable bolus back that canserve to enhance the accuracy of the calibration phantom by accountingfor the effect of soft tissue that may project with the calibrationphantom and/or with the bone.

In certain embodiments, the calibration phantom can be configured sothat it stabilizes against the surrounding tissues on its own withoutthe use of an additional holder. The calibration phantom can beprotected with a hygienic cover.

The holder (e.g., hygienic cover) may be comprised of a rigid material,a flexible material or combinations thereof. Furthermore, the holder mayinclude one or more pockets/compartments adapted to receive additionalcomponents such as the calibration phantom, a bolus back or the like.Additionally, one or more portions of the holder may be radiolucent.

2.0. Analysis and Manipulation of Data

The data obtained from images taken as described above is thenpreferably analyzed and manipulated. Thus, the systems and assembliesdescribed herein can also include one or more computational unitsdesigned, for example, to analyze bone density or bone structure ormacro-anatomical and/or biomechanical data in the image; to identify ananatomical landmark in an anatomical region; to correct for soft tissuemeasurements; and/or to evaluate bone density and structure andmacro-anatomy of the image. As will be appreciated by those of skill inthe art, the computational unit can include any software, chip or otherdevice used for calculations. Additionally, the computational unit maybe designed to control the imaging assembly or detector (as well asother parameters related to the detector(s)). Other applications of thecomputational unit to the methods and devices described herein will berecognized by those skilled in the art. The computational unit may beused for any other application related to this technology that may befacilitated with use of computer software or hardware. The computationalunit can also further comprise a database comprising, for example,reference anatomical maps and the computational unit is further designedto compare the anatomical map with the reference anatomical map. Thereference anatomical map may be historic (from the same or anotherpatient, generated as part of an interrogation protocol), or theoreticalor any other type of desired reference map.

Any image can be analyzed in order to obtain and manipulate data. Thus,data points, derived data, and data attributes database according to thepresent invention may comprise the following: (1) the collection of datapoints, said data points comprising information obtained from an image,for example, bone mineral density information or information on bonestructure (architecture); and (2) the association of those data pointswith relevant data point attributes. The method may further comprise (3)determining derived data points from one or more direct data points and(4) associating those data points with relevant data point attributes.The method may also comprise (5) collection of data points using aremote computer whereby said remote computer operates in a networkenvironment.

In certain preferred embodiments, the information is obtained from adental x-ray image. As described herein, dental x-ray images can beacquired at a local site using known techniques. If the x-ray image wascaptured using conventional x-ray film, the data points (information) ofthe x-ray image can be digitized using a scanning device. The digitizedx-ray image information can then be transmitted over the network, e.g.the Internet, into a remote computer or server. If the x-ray image wasacquired using digital acquisition techniques, e.g. using phosphorusplate systems or selenium or silicon detector systems, the x-ray imageinformation is already available in digital format. In this case theimage can be transmitted directly over the network, e.g. the Internet.The information can also be compressed and/or encrypted prior totransmission. Transmission can also be by other methods such as fax,mail or the like.

2.1. Data Points

Thus, the methods of and compositions described herein make use ofcollections of data sets of measurement values, for example measurementsof bone structure and/or bone mineral density from x-ray images. Recordsmay be formulated in spreadsheet-like format, for example including dataattributes such as date of x-ray, patient age, sex, weight, currentmedications, geographic location, etc. The database formulations mayfurther comprise the calculation of derived or calculated data pointsfrom one or more acquired data points. A variety of derived data pointsmay be useful in providing information about individuals or groupsduring subsequent database manipulation, and are therefore typicallyincluded during database formulation. Derived data points include, butare not limited to the following: (1) maximum bone mineral density,determined for a selected region of bone or in multiple samples from thesame or different subjects; (2) minimum bone mineral density, determinedfor a selected region of bone or in multiple samples from the same ordifferent subjects; (3) mean bone mineral density, determined for aselected region of bone or in multiple samples from the same ordifferent subjects; (4) the number of measurements that are abnormallyhigh or low, determined by comparing a given measurement data point witha selected value; and the like. Other derived data points include, butare not limited to the following: (1) maximum value of a selected bonestructure parameter, determined for a selected region of bone or inmultiple samples from the same or different subjects; (2) minimum valueof a selected bone structure parameter, determined for a selected regionof bone or in multiple samples from the same or different subjects; (3)mean value of a selected bone structure parameter, determined for aselected region of bone or in multiple samples from the same ordifferent subjects; (4) the number of bone structure measurements thatare abnormally high or low, determined by comparing a given measurementdata point with a selected value; and the like. Other derived datapoints include, but are not limited to the following: (1) maximum valueof a selected macro-anatomical and/or biomechanical parameter,determined for a selected region of bone or in multiple samples from thesame or different subjects; (2) minimum value of a selectedmacro-anatomical and/or biomechanical parameter, determined for aselected region of bone or in multiple samples from the same ordifferent subjects; (3) mean value of a selected macro-anatomical and/orbiomechanical parameter, determined for a selected region of bone or inmultiple samples from the same or different subjects; (4) the number ofmacro-anatomical and/or biomechanical measurements that are abnormallyhigh or low, determined by comparing a given measurement data point witha selected value; and the like. Other derived data points will beapparent to persons of ordinary skill in the art in light of theteachings of the present specification. The amount of available data anddata derived from (or arrived at through analysis of) the original dataprovide provides an unprecedented amount of information that is veryrelevant to management of bone related diseases such as osteoporosis.For example, by examining subjects over time, the efficacy ofmedications can be assessed.

Measurements and derived data points are collected and calculated,respectively, and may be associated with one or more data attributes toform a database. The amount of available data and data derived from (orarrived at through analysis of) the original data provide provides anunprecedented amount of information that is very relevant to managementof bone related diseases such as osteoporosis. For example, by examiningsubjects over time, the efficacy of medications can be assessed.

Data attributes can be automatically input with the x-ray image and caninclude, for example, chronological information (e.g., DATE and TIME).Other such attributes may include, but are not limited to, the type ofx-ray imager used, scanning information, digitizing information and thelike. Alternatively, data attributes can be input by the subject and/oroperator, for example subject identifiers, i.e. characteristicsassociated with a particular subject. These identifiers include but arenot limited to the following: (1) a subject code (e.g., a numeric oralpha-numeric sequence); (2) demographic information such as race,gender and age; (3) physical characteristics such as weight, height andbody mass index (BMI); (4) selected aspects of the subject's medicalhistory (e.g., disease states or conditions, etc.); and (5)disease-associated characteristics such as the type of bone disorder, ifany; the type of medication used by the subject. In the practice of thepresent invention, each data point would typically be identified withthe particular subject, as well as the demographic, etc. characteristicof that subject.

Other data attributes will be apparent to persons of ordinary skill inthe art in light of the teachings of the present specification.

2.2. Storage of Data Sets and Association of Data Points with RelevantData Attributes

A number of formats exist for storing data sets and simultaneouslyassociating related attributes, including but not limited to (1)tabular, (2) relational, and (3) dimensional. In general the databasescomprise data points, a numeric value which correspond to physicalmeasurement (an “acquired” datum or data point) or to a single numericresult calculated or derived from one or more acquired data points thatare obtained using the various methods disclosed herein. The databasescan include raw data or can also include additional related information,for example data tags also referred to as “attributes” of a data point.The databases can take a number of different forms or be structured in avariety of ways.

The most familiar format is tabular, commonly referred to as aspreadsheet. A variety of spreadsheet programs are currently inexistence, and are typically employed in the practice of the presentinvention, including but not limited to Microsoft Excel spreadsheetsoftware and Corel Quattro spreadsheet software. In this format,association of data points with related attributes occurs by entering adata point and attributes related to that data point in a unique row atthe time the measurement occurs.

Further, rational, relational (Database Design for Mere Mortals, byMichael J. Hernandez, 1997, Addison-Wesley Pub. Co., publisher; DatabaseDesign for Smarties, by Robert J. Muller, 1999, Morgan KaufmannPublishers, publisher; Relational Database Design Clearly Explained, byJan L. Harrington, 1998, Morgan Kaufmann Publishers, publisher) anddimensional (Data-Parallel Computing, by V. B. Muchnick, et al., 1996,International Thomson Publishing, publisher; Understanding FourthDimensions, by David Graves, 1993, Computerized Pricing Systems,publisher) database systems and management may be employed as well.

Relational databases typically support a set of operations defined byrelational algebra. Such databases typically include tables composed ofcolumns and rows for the data included in the database. Each table ofthe database has a primary key, which can be any column or set ofcolumns, the values for which uniquely identify the rows in a table. Thetables in the database can also include a foreign key that is a columnor set of columns, the values of which match the primary key values ofanother table. Typically, relational databases also support a set ofoperations (e.g., select, join and combine) that form the basis of therelational algebra governing relations within the database.

Such relational databases can be implemented in various ways. Forinstance, in Sybase® (Sybase Systems, Emeryville, Calif.) databases, thetables can be physically segregated into different databases. WithOracle® (Oracle Inc., Redwood Shores, Calif.) databases, in contrast,the various tables are not physically separated, because there is oneinstance of work space with different ownership specified for differenttables. In some configurations, databases are all located in a singledatabase (e.g., a data warehouse) on a single computer. In otherinstances, various databases are split between different computers.

It should be understood, of course, that the databases are not limitedto the foregoing arrangements or structures. A variety of otherarrangements will be apparent to those of skill in the art.

2.3. Data Manipulation

Data obtained from x-ray images as described herein can be manipulated,for example, using a variety of statistical analyses, to produce usefulinformation. The databases of the present invention may be generated,for example, from data collected for an individual or from a selectedgroup of individuals over a defined period of time (e.g., days, monthsor years), from derived data, and from data attributes.

For example, data may be aggregated, sorted, selected, sifted, clusteredand segregated by means of the attributes associated with the datapoints. A number of data mining software programs exist which may beused to perform the desired manipulations.

Relationships in various data can be directly queried and/or the dataanalyzed by statistical methods to evaluate the information obtainedfrom manipulating the database.

For example, a distribution curve can be established for a selected dataset, and the mean, median and mode calculated therefor. Further, dataspread characteristics, e.g. variability, quartiles and standarddeviations can be calculated.

The nature of the relationship between any variables of interest can beexamined by calculating correlation coefficients. Useful methods fordoing so include but are not limited to the following: Pearson ProductMoment Correlation and Spearman Rank Order Correlation.

Analysis of variance permits testing of differences among sample groupsto determine whether a selected variable has a discernible effect on theparameter being measured.

Non-parametric tests may be used as a means of testing whethervariations between empirical data and experimental expectancies areattributable merely to chance or to the variable or variables beingexamined. These include the Chi Square test, the Chi Square Goodness ofFit, the 2×2 Contingency Table, the Sign Test, and the Phi CorrelationCoefficient.

There are numerous tools and analyses available in standard data miningsoftware that can be applied to the analysis of the databases of thepresent invention. Such tools and analyses include, but are not limitedto, cluster analysis, factor analysis, decision trees, neural networks,rule induction, data driven modeling, and data visualization. Some ofthe more complex methods of data mining techniques are used to discoverrelationships that are more empirical and data-driven, as opposed totheory-driven, relationships.

Exemplary data mining software that can be used in analysis and/orgeneration of the databases of the present invention includes, but isnot limited to: Link Analysis (e.g., Associations analysis, SequentialPatterns, Sequential time patterns and Bayes Networks); Classification(e.g., Neural Networks Classification, Bayesian Classification,k-nearest neighbors classification, linear discriminant analysis, Memorybased Reasoning, and Classification by Associations); Clustering (e.g.,k-Means Clustering, demographic clustering, relational analysis, andNeural Networks Clustering); Statistical methods (e.g., Means, Std dev,Frequencies, Linear Regression, non-linear regression, t-tests, F-test,Chi2 tests, Principal Component Analysis, and Factor Analysis);Prediction (e.g., Neural Networks Prediction Models, Radial BasedFunctions predictions, Fuzzy logic predictions, Times Series Analysis,and Memory based Reasoning); Operating Systems; and Others (e.g.,Parallel Scalability, Simple Query Language functions, and C++ objectsgenerated for applications). Companies that provide such softwareinclude, for example, the following: Adaptative Methods Group at UTS(UTS City Campus, Sydney, NSW 2000), CSI®, Inc., (Computer ScienceInnovations, Inc. Melbourne, Fla.), IBM® (International BusinessMachines Corporation, Armonk, N.Y.), Oracle (Oracle Inc., RedwoodShores, Calif.) and SAS® (SAS Institute Inc., Cary, N.C.).

These methods and processes may be applied to the data obtained usingthe methods described herein, for example, databases comprising, x-rayimage data sets, derived data, and data attributes.

In certain embodiments, data (e.g., bone structural information ormacro-anatomical and/or biomechanical information or bone mineraldensity information) is obtained from normal control subjects using themethods described herein. These databases are typically referred to as“reference databases” and can be used to aid analysis of any givensubject's x-ray image, for example, by comparing the informationobtained from the subject to the reference database. Generally, theinformation obtained from the normal control subjects will be averagedor otherwise statistically manipulated to provide a range of “normal”(reference) measurements. Suitable statistical manipulations and/orevaluations will be apparent to those of skill in the art in view of theteachings herein.

ADD z-score, T-scores here; other statistical measurements that you deemimportant. The comparison of the subject's x-ray information to thereference database can be used to determine if the subject's boneinformation falls outside the normal range found in the referencedatabase or is statistically significantly different from a normalcontrol. Data comparison and statistical significance can be readilydetermined by those of skill in the art using for example the z-test ort-test statistics for continuous variables, the chi-square test orFisher's exact test for categorical data and the rank-sum test orKruskal-Wallis test for ranked data. The use of reference databases inthe analysis of x-ray images facilitates that diagnosis, treatment andmonitoring of bone conditions such as osteoporosis.

For a general discussion of statistical methods applied to dataanalysis, see Applied Statistics for Science and Industry, by A. Romano,1977, Allyn and Bacon, publisher.

The data is preferably stored and manipulated using one or more computerprograms or computer systems. These systems will typically have datastorage capability (e.g., disk drives, tape storage, CD-ROMs, etc.).Further, the computer systems may be networked or may be stand-alonesystems. If networked, the computer system would be able to transferdata to any device connected to the networked computer system forexample a medical doctor or medical care facility using standard e-mailsoftware, a central database using database query and update software(e.g., a data warehouse of data points, derived data, and dataattributes obtained from a large number of subjects). Alternatively, auser could access from a doctor's office or medical facility, using anycomputer system with Internet access, to review historical data that maybe useful for determining treatment.

If the networked computer system includes a World Wide Web application,the application includes the executable code required to generatedatabase language statements, for example, SQL statements. Suchexecutables typically include embedded SQL statements. The applicationfurther includes a configuration file that contains pointers andaddresses to the various software entities that are located on thedatabase server in addition to the different external and internaldatabases that are accessed in response to a user request. Theconfiguration file also directs requests for database server resourcesto the appropriate hardware, as may be necessary if the database serveris distributed over two or more different computers.

Usually each networked computer system includes a World Wide Web browserthat provides a user interface to the networked database server. Thenetworked computer system is able to construct search requests forretrieving information from a database via a Web browser. With access toa Web browser users can typically point and click to user interfaceelements such as buttons, pull down menus, and other graphical userinterface elements to prepare and submit a query that extracts therelevant information from the database. Requests formulated in thismanner are subsequently transmitted to the Web application that formatsthe requests to produce a query that can be used to extract the relevantinformation from the database.

When Web-based applications are utilized, the Web application accessesdata from a database by constructing a query in a database language suchas Sybase or Oracle SQL which is then transferred to a relationaldatabase management system that in turn processes the query to obtainthe pertinent information from the database.

Accordingly, in one aspect the present invention describes a method ofproviding data obtained from x-ray images on a network, for example theInternet, and methods of using this connection to provide real-time anddelayed data analysis. The central network can also allow access by thephysician to a subject's data. Similarly, an alert could be sent to thephysician if a subject's readings are out of a predetermined range, etc.The physician can then send advice back to the patient via e-mail or amessage on a web page interface. Further, access to the entire databaseof data from all subjects may be useful for statistical or researchpurposes. Appropriate network security features (e.g., for datatransfer, inquiries, device updates, etc.) are of course employed.

Further, a remote computer can be used to analyze the x-ray that hasbeen transmitted over the network automatically. For example, x-raydensity information or structural information about an object can begenerated in this fashion. X-ray density information can, for example,be bone mineral density. If used in this fashion, the test can be usedto diagnose bone-related conditions such as osteoporosis.

2.4. Graphical User Interface

In certain of the computer systems, an interface such as an interfacescreen that includes a suite of functions is included to enable users toeasily access the information they seek from the methods and databasesof the invention. Such interfaces usually include a main menu page fromwhich a user can initiate a variety of different types of analyses. Forexample, the main menu page for the databases generally include buttonsfor accessing certain types of information, including, but not limitedto, project information, inter-project comparisons, times of day,events, dates, times, ranges of values, etc.

2.5. Computer Program Products

A variety of computer program products can be utilized for conductingthe various methods and analyses disclosed herein. In general, thecomputer program products comprise a computer-readable medium and thecode necessary to perform the methods set forth supra. Thecomputer-readable medium on which the program instructions are encodedcan be any of a variety of known medium types, including, but notlimited to, microprocessors, floppy disks, hard drives, ZIP drives, WORMdrives, magnetic tape and optical medium such as CD-ROMs.

For example, once an image or data from that image is transmitted via alocal or long-distance computer network and the data received by aremote computer or a computer connected to the remote network computer,an analysis of the morphology and density of the bone can be performed,for example using suitable computer programs. This analysis of theobject's morphology can occur in two-dimensions or three-dimensions. Forexample, in imaging osseous structures, such analysis of the transmittedx-ray image can be used to measure parameters that are indicative orsuggestive of bone loss or metabolic bone disease. Such parametersinclude all current and future parameters that can be used to evaluateosseous structures. For example, such parameters include, but are notlimited to, trabecular spacing, trabecular thickness, trabecularconnectivity and intertrabecular space.

Information on the morphology or 2D or 3D structure of an anatomicobject can be derived more accurately, when image acquisition parameterssuch as spatial resolution are known. Other parameters such as thedegree of cone beam distortion can also be helpful in this setting.

As noted above, an image can be transmitted from a local site into aremote server and the remote server can perform an automated analysis ofthe image. Further, the remote server or a computer connected to theremote server can then generate a diagnostic report. Thus, in certainembodiments, a computer program (e.g., on the remote server or on acomputer connected to the remote server) can generate charges for thediagnostic report. The remote server can then transmit the diagnosticreport to a physician, typically the physician who ordered the test orwho manages the patient. The diagnostic report can also be transmittedto third parties, e.g. health insurance companies. Such transmission ofthe diagnostic report can occur electronically (e.g. via e-mail), viamail, fax or other means of communication. All or some of thetransmitted information (e.g., patient identifying information) can beencrypted to preserve confidentiality of medical records.

Thus, one exemplary system is described herein for analyzing bonemorphology or structure in a subject system via a dental x-ray thatincludes at least a portion of the mandible and/or maxilla of a subject,followed by evaluation or the x-ray image. Dental x-rays are obtained inany conventional method. The x-ray produces an image that can beinterpreted (for example, employing a selected algorithm and/or computerprogram) by an associated system controller to provide a bone mineraldensity or bone structure evaluation for display.

In a further aspect of the present invention, the monitoring system cancomprise two or more components, in which a first component comprises anx-ray image and calibration phantom that are used to extract and detectbone-related data on the subject, and a second component that receivesthe data from the first component, conducts data processing on the dataand then displays the processed data. Microprocessor functions can befound in one or both components. The second component of the monitoringsystem can assume many forms

3.0.0.0 Correction Factors

Although the presence of calibration phantoms greatly aids in increasingthe accuracy of data obtained from images such as dental, hip or spinex-rays, the present inventors also recognize that, in certain instances,there may be a need to apply one or more correction factors to furtherenhance accuracy of the data obtained from any given x-ray image. Suchcorrection factors will take into account one or more of a wide varietyof influences (e.g., soft tissue thickness, region from which the datais extracted and the like) that can alter apparent density or structureinformation on the image.

In this regard, one or more reference databases can be used forcalibration and normalization purposes. For example, image normalizationor correction of soft-tissue attenuation can be performed using patientcharacteristic data such as patient weight, height and body mass index.In one example, a higher soft-tissue attenuation can be assumed in highweight and low height subjects; a lower soft-tissue attenuation will beassumed in low weight and high height subjects.

In another embodiment, a standard calibration curve is applied to x-rayimages, whereby said calibration curve can be derived from referencex-rays obtained with use of calibration phantoms. For example, 100patients can undergo dental x-rays with a calibration phantom and astandard calibration curve can be derived from these images. Similarly,100 patients can undergo hip x-rays with a calibration phantom and astandard calibration curve can be derived from these images. Differentcalibration curves can be generated for different populations, forexample, by generating different calibration curves for different rangesin body mass index, body height, sex, race etc.

3.1.0.0. Anatomical Landmarks

In one embodiment, identification of anatomic landmarks of the structureto be analyzed or identification of anatomical landmarks adjacent to thestructure to be analyzed with subsequent positioning and computeranalysis of the x-ray image relative to these anatomic landmarks or withsubsequent positioning and computer analysis of anatomical region ofinterest (ROI) relative to these anatomic landmarks is performed. Thepresent invention includes also positioning dental or other x-raydetectors, positioning the dental or other x-ray tube, and analyzing theresulting images using landmarks based on either 1) texturalinformation, 2) structural information, 3) density information (e.g.density), or 4) 2 or 3 dimensional contour information 5) a combinationsthereof of the tissue or structure to be measured and of tissues orstructures adjacent to the measurement site. The invention also includesmethods and devices that are not necessarily based solely on anatomicallandmarks, but in some applications can be combined with anatomicallandmark embodiments. Preferably, many of the embodiments describedherein are designed for automated use with a minimum of operatorintervene and preferably remote or computer control of such devices.

In one embodiment, an alignment device may be used to ensureperpendicular or near perpendicular alignment of the dental or otherx-ray tube relative to the x-ray film, thereby decreasing geometricdistortion resulting from tube angulation. For example, an x-ray filmholder is positioned relative to an anatomical landmark, e.g. theposterior wall of the mandible in the incisor region. A side-view of anexemplary alignment system using a dental x-ray film holder is shown inFIG. 15. The system includes bite block (100), stainless steel rod(101), film (103), optional calibration phantom (104), Rinn holder (102)typically having a ring or donut shape, and extension tubing (200). Theextension tubing is designed to fit within the Rinn holder and may betemporarily or permanently attached. The system can achieve highreproducibility of the film position relative to an anatomical landmarksuch as the alveolar ridge or the posterior wall of the mandible. Theextension tubing allows for alignment of the x-ray tube so that it isnear perpendicular to the Rinn instrument and, ultimately, the dentalfilm.

Since manual alignment of the dental x-ray tube, namely the tube (e.g.,metal) located in front of the dental x-ray tube for pointing andalignment purposes, is often not very accurate with alignment errors of3, 5 or even more degrees, a mechanical or electromagnetic device ispreferably used in order to achieve perpendicular or near perpendicularalignment between the metal tube anterior to the x-ray tube and the Rinnholder. For example, the metal tube can be physically attached to theRinn holder with use of one or more Velcro™ straps or it can be alignedusing optical aids such as levels, cross-hairs, light sources (points orareas), etc. Alternatively, such physical attachment can be achievedwith use of one or more magnets rigidly attached to the dental x-raysystem metal tube and the Rinn holder. In this embodiment, the magnetson the Rinn holder and the dental x-ray system metal tube will bealigned and brought into physical contact. In another embodiment, anextension tube is attached, for example with an adhesive, to the Rinnholder. The extension tubing can also be an integral part of the Rinnholder. The extension tubing can be designed so that its inner diameteris slightly greater than the outer diameter of the dental x-ray systemmetal tube. The dental x-ray system metal tube is then inserted into theextension tubing attached to the Rinn holder thereby greatly reducingalignment error of the x-ray tube relative to the x-ray film.Alternatively, the extension tubing can be designed so that its outerdiameter is slightly smaller than the inner diameter of the dental x-raysystem metal tube. The dental x-ray system metal tube is then advancedover the extension tubing attached to the Rinn holder thereby greatlyreducing alignment error of the x-ray tube relative to the x-ray film.One of skill in the art will easily recognize in view of the teachingsherein that many other attachment means can be used for properlyaligning the dental x-ray tube with the dental x-ray film. Combinationsof attachment mechanisms are also possible.

The anatomical landmark that is selected is part of an anatomicalregion. An anatomical region refers to a site on bone, tooth or otherdefinable biomass that can be identified by an anatomical feature(s) orlocation. An anatomical region can include the biomass underlying thesurface. Usually, such a region will be definable according to standardmedical reference methodology, such as that found in Williams et al.,Gray's Anatomy, 1980. The anatomical region can be selected from thegroup consisting of an edge of the mandible, an edge of the maxilla, anedge of a tooth, valleys or grooves in any of these structures orcombinations thereof. The dental x-ray image can be readily taken so asto include the anatomical site. Other anatomical regions include but arenot limited to the hip, the spine, the forearm, the foot, and the knee.

For example, the region of interest is placed between the dental apicesand the inferior mandibular cortex. The apices can be foundautomatically in the following way: for each row of pixels, the grayvalue profile is examined. While a profile that intersects bone anddental roots in an alternating fashion has several distinct peaks andvalleys, a profile that only covers trabecular bone shows irregularchanges in the gray values (FIG. 6). The dental apices are located inthe transitional region between these two patterns.

The measurement techniques to assess trabecular bone structure ormacro-anatomical and/or biomechanical parameters are preferably designedto work without user intervention. In order to fully automate theprocess of analyzing dental x-rays, it is necessary to develop atechnique to locate the regions of interest (ROIs) that are used for thecalculation of the structural parameters of the trabecular bone. If theprofile for a particular row of pixels contains distinct peaks, theirnumber, width and height can be determined. Next, the rows below theselines can be evaluated until the peaks have disappeared. This linedetermines the boundary, 5 mm below which the ROI can be placed in thecenter between the longitudinal axes of the roots, which can also bedetermined from the row profiles (FIG. 6). At a pixel size of 0.042mm×0.042 mm, which corresponds to a resolution of 600 dpi, the ROI has asize of 5.4 mm×5.4 mm (128×128 pixels). For other scanning resolutions,the pixel resolution of the ROI can be adjusted accordingly.

In the case of an edentulous patient, bone mineral density can bemeasured in all ROIs that are located on a line that is, for example, 8mm inferior and parallel to the alveolar ridge. The ROIs can be movedfrom left to right on a pixel-by-pixel basis. Eventually, the ROI withthe lowest BMD can be chosen for further evaluation of the structuralbone parameters. This helps to avoid inclusion of regions on the x-raywhere bone mineral density may be overestimated due to projection of thecurved parts of the mandible near the canine teeth. Alternatively, theROI with the median BMD can be used. Other statistical parameters can beemployed for this purpose.

Thus, software or other computational unit can identify the selectedanatomic landmark in an interrogated x-ray image and direct analysis ofthe image using various parameters and analytic functions. Further, suchsoftware or other computational analytical unit can be used to identifyareas of particular density at a certain distance from the selectedlandmark. Similarly, manual or computer analysis can be used to identifyareas of lowest, highest, median or average density (or structuralcharacteristics) in relation to the selected landmark.

Further, the same landmark may be compared at different times(intra-landmark comparison) or one or more landmarks may be compared(inter-landmark comparison). For instance, an intra-landmark comparisoncan be used during a single interrogation protocol that entails multipleinterrogations of the same region with reference to a particularanatomical landmark. Statistical analysis as described herein and knownin the art can be performed.

Thus, the invention provides for means of assessing bone structure, i.e.the two-dimensional or three-dimensional architectural organization ofthe trabecular bone including, but not limited to, measurement oftrabecular spacing, trabecular thickness, trabecular length andtrabecular connectivity. Other examples of measurements of bonestructure are provided in TABLE 1. These measurements can be used aloneor enhanced with use of calibration phantoms or external standards thatcan allow a correction or normalization of image intensity and that canin certain embodiments also allow a correction of geometric distortionsfor example resulting from cone beam geometry of an x-ray beam.

The invention provides for means of assessing macro-anatomical and/orbiomechanical parameters. These measurements can be used alone orenhanced with use of calibration phantoms or external standards that canallow a correction or normalization of image intensity and that can incertain embodiments also allow a correction of geometric distortionsincluding magnification, for example resulting from cone beam geometryof an x-ray beam.

As described herein, one or more measurements of bone structure ormacro-anatomical and/or biomechanical parameters can be used to select atherapy, for example the use of anabolic or antiresorptive agent in thecase of bone loss or deterioration. In certain embodiments, measurementsof bone structure and/or one or more macro-anatomical and/orbiomechanical parameters are conducted over time to longitudinallymonitor a subject's bone health longitudinally over time. Measurementscan be performed at different time points T1, T2, . . . , Tn and changesin said bone structure and/or macro-anatomical and/or biomechanicalparameters can be registered and used to track a patient's bone health.In either single or longitudinally measurements, a physician can beapprised of the measurements and can include a pre-determined cut-offvalue (e.g., when a bone structure or macro-anatomical and/orbiomechanical parameter measured in a patient is more than one or twostandard deviations different from a normal, healthy referencepopulation) and use this information to select a therapy.

The data obtained and analyzed as described herein can be used tomonitor a patient's response to therapy. For example, informationregarding bone structural and/or macro-anatomical and/or biomechanicalinformation in a patient receiving an anabolic or antiresorptive drugand be evaluated at different time intervals T1, T2, . . . , Tn andchanges in said bone structure and/or macro-anatomical and/orbiomechanical parameters can be used in order to assess therapeuticefficacy. A physician can use this information to adjust the dose of adrug administered (e.g., for treatment of osteoporosis) or to change thedrug regimen.

Other techniques using x-ray information such as tomosynthesis can alsobe used for measuring bone structure and for selecting said therapy ormonitoring said therapy.

Bone structure can be measured using a number of different technicalapproaches. These include but are not limited to the Hough Transform,analysis of density and size distribution of trabeculae,multidimensional classification schemes, mean pixel intensity, varianceof pixel intensity, Fourier spectral analysis, fractal dimension andmorphological parameters.

3.1.1.0. Hough Transform

The Hough transform (See, e.g., Hough “Machine analysis of bubblechamber pictures” in International Conference on High EnergyAccelerators and Instrumentation. 1959. CERN) can be used to detectgeometric objects in binary images. As an entirely new approach toassessing bone structure and/or macro-anatomical, the invention includesthe use of such methods to analyze direction and length of structures inbone images. For this purpose, the region of interest (ROI) can beblurred with a Gaussian filter. The pixel values of the filtered ROI canthen be subtracted from those in the original ROI, and the value 128 canbe added at each pixel location. This results in an image with a meangray value of 128, which is also used as a threshold to yield a binaryimage in which the trabeculae are represented by the white pixels.

After a skeletonization step, a Hough transform with the lineparameterization ρ=x cos θ+y sin θ can be applied to the binary image inorder to find straight line segments. Here ρ is the perpendiculardistance of the line from the origin and θ is the angle between thex-axis and the normal. Each point ({circumflex over (x)},ŷ) in theoriginal image is transformed into a sinusoidal curve ρ={circumflex over(x)} cos θ+ŷ sin θ in the (ρ,θ) plane of the transformed image (see FIG.7)). Ideally, the curves from collinear points in the original imageintersect in a single point in the transformed image. However, the (ρ,θ)plane can be divided into bins, where each bin counts the number oftransformed curves that pass through it. This number corresponds to thenumber of collinear points on a line segment in the original image, andthus the length of this segment. Furthermore, the transformed imageprovides information on the predominant angles of the line segments inthe original image (see FIG. 8).

The average length and the variance of the line segments, which arecalculated for all bins with a count above a certain threshold, can beused as structural parameters for the shape of the bone trabeculae.Average length as well as the variability of the length to decrease inpatients with osteoporosis. The threshold has the effect that onlysegments of a certain minimal length are included in the calculation.Choosing the threshold so that it provides the best discriminationbetween healthy and diseased individuals can be readily determined byone of skill in the art in view of the teachings herein.

The “center of mass” of the transformed image h, given as:

${{C\; M} = {\left( {\sum\limits_{({\rho,\theta})}{\left( {\rho,\theta} \right)^{T}*{H\left( {\rho,\theta} \right)}}} \right)/{\sum\limits_{({\rho,\theta})}{H\left( {\rho,\theta} \right)}}}},$in which each bin is interpreted as an element with a mass equivalent toits count, is a way to measure the predominant angles of the trabecularsegments. The angle at cm is measured with respect to the alveolar rimto obtain a standardized value. More importantly, the variance of thesegment angles (again measured after thresholding the bin counts)provides information on the anisotropy of the trabecular structure.Histomorphological studies of osteoporotic vertebrae have shown that thevariability of trabecular orientations decreases with the disease.

3.1.2.0. Analysis of Density and Size Distribution of Trabeculae

Morphological operations such as variations of dilation and erosion andcombinations thereof can also be used to detect the size of structuresin gray scale or binary images. For example, a skeleton operator can beused to extract and quantify trabeculae of different sizes anddirections, which results in a measure of the size distribution oftrabecular structures. This skeleton operator is based on the workdescribed in Kumasaka et al. (1997) Dentomaxillofac Rad 26:161-168 andworks as follows:

Let a two-dimensional structuring element e be a function over thewindow −m≦i,j≦m(m>0) with E(i,j)ε{0,1}. The dilation operator sets apixel value f(x,y) in a gray scale image f to the maximum of thosevalues within the window of size m, for which e(i,j)=1:

${\left\lbrack {f \oplus E} \right\rbrack\left( {x,y} \right)} = {\max\limits_{{{- m} \leq i},{j \leq m}}\left\{ {{{f\left( {{x + i},{y + j}} \right)}❘{E\left( {i,j} \right)}} = 1} \right\}}$

The erosion operator is defined accordingly, using the minimum insteadof the maximum:

${\left\lbrack {f \otimes E} \right\rbrack\left( {x,y} \right)} = {\min\limits_{{{- m} \leq i},{j \leq m}}\left\{ {{{f\left( {{x + i},{y + j}} \right)}❘{E\left( {i,j} \right)}} = 1} \right\}}$

‘Opening’ is the operation of maximum search after minimum search:f _(E)=(f

E)⊕E

Accordingly, the ‘closing’ operation is defined as the minimum searchafter maximum search:f ^(E)=(f⊕E)

E

If a fixed structuring element E₁ is given as E₁(ij)=1 for −1≦i,j≦1, theskeleton operation is then defined asS _(Trabeculae)(f)=(f

E ₂)−[(f

E ₂)_(E) ₁ ]  (1)

E₂ is another structuring element that is of circular shape and can bevaried in size, and therefore renders the skeleton operator sensitive tothe size of the structures in the image. The erosion of f with E₂ erasesthe structures that are smaller than E₂ and extracts those trabeculaethat are at least equal in size. Those structures that are exactly equalin size is reduced to a width of one pixel. The opening step with E₁causes all structures that are one pixel wide to disappear (second termin (1)). After subtraction of this term from the first one, only thosetrabecular structures that exactly match the size of E₂ remain. Finally,the image is thresholded with a level of 1. The effect of this operatoris illustrated in FIG. 9.

FIG. 10 demonstrates the use of the skeleton operator with the samestructural element diameters as in FIG. 9 on a gray scale region ofinterest from a dental x-ray containing trabecular bone. The number ofbright pixels in the binary images resulting from each skeletonoperation corresponds to the portion of trabeculae of the particularsize in the original image. If the percentage of the bright pixels withrespect to the total number of pixels in each skeletonized image isplotted against the diameter of E₂, the “center of mass” of the curve,i.e. the predominant structure size, can be used as an index todiscriminate between osteoporotic and healthy bone.

Furthermore, the skeleton operator is preferably optimized and extendedto detect structures that are oriented only in a specific direction.This can be achieved by adding erosion operations to the skeletonoperator with structural elements in which, for example, only thediagonal pixels are set to 1.

This can be used to calculate an anisotropy index, similar to the onederived from the Hough transform. Both anisotropy indices are testedwith respect to their potential to distinguish healthy from osteoporoticbone.

In a similar manner the sizes of the marrow spaces can be examined. Theskeleton operator is then defined asS _(Marrow)(f)=(f⊕E ₂)−[(f⊕E ₂)^(E) ¹ ]

In addition, the watershed segmentation can be applied to backgroundsubtracted gray level structures on x-ray images to characterize thehomogeneity of trabecular structures. This process takes into accountthe gray level contrast between structures to define marrow spaces. Thewatershed segmentation, when applied to background subtracted bone x-rayimages, defines regions with lower gray levels (or basins) surrounded byhigher gray level structures (or ridges), as marrow space, in accordanceto the spatial extend and gray levels of ridges. Therefore, the size andorientation of marrow space segments defined by this procedure can berelated to the spacing, relative density and orientation of adjacenttrabecular structures. The segments of marrow space generated using thewatershed segmentation can be measured for their area, eccentricity,orientation, and the average gray level on the x-ray image within thesegment. The statistics (for example mean, standard deviation, minimum,maximum, and mode) for each of the segment characteristics can bemeasured. These statistics can be selected to reflect the homogeneity ofmarrow space and trabecular structures, and can be used to detectpresence of abnormal distribution of marrow space and trabecularstructures.

3.1.3.0. Multidimensional Classification Schemes

In certain embodiments, it is preferred to use multiple indices tomeasure bone structure and/or macro-anatomical parameters. Thus, novelapproaches that integrate one or more suitable indices can be employed.The indices can be optimized and incorporated into a multi-dimensionalclassification scheme, for example using a nearest neighborclassification. Cover et al. (1967) IEEE Trans Inform Theory 13(1):21-7.(See, Example 3).

Table 1 provides examples of different analyses andanatomical/physiological correlates of the parameters that can bemeasured.

TABLE 1 Analysis Anatomical/Physiological Correlates Hough transformlength and direction of trabeculae; anisotropy Morphological thicknessand direction of trabeculae; anisotropy; operators thickness and lengthof marrow spaces Mean pixel intensity bone mineral density Variance ofpixel complexity of trabecular structure intensity Fourier spectralcomplexity of trabecular structure analysis Fractal dimension complexityof trabecular structure Morphological length, size of trabeculae;complexity of trabecular parameters structure; length, size of marrowspaces; complexity of marrow space

3.1.3.1 Mean Pixel Intensity

Mean pixel intensity is a general parameter for the bone mineraldensity. The degree to which x-rays passing through bone tissue areabsorbed depends on the bone's mineral content. Bone with a highermineral density absorbs a larger portion of x-rays, and thereforeappears brighter on an x-ray image.

The mean pixel intensity f(x,y) in the ROI is calibrated against analuminum calibration wedge that is included in the image. The log of theaverage pixel intensity for each thickness level of the calibrationwedge is plotted against the thickness, which allows f(x,y) to beconverted into a standardized aluminum thickness equivalent, which isused as the value for this parameter. The automatic recognition of thedifferent thickness levels of the calibration wedge are made possible bydifferent geometric patterns scribed into the wedge which are shown inthe x-ray image and can be localized automatically.

3.1.3.2. Variance of Pixel Intensity

The variance of the pixel gray values in the ROI, var f(x,y), describesthe variability of the pixel intensities and can therefore be a measureof the degree of trabeculation. A loss of trabecular bone is predictedto be reflected by a decreased var f(x,y). Southard & Southard (1992)Oral Surg Oral Med Oral Pathol 74:111-117.

3.1.3.3. Fourier Spectral Analysis

The spatial frequency spectrum of a texture provides information aboutits coarseness. Fine textural structures and edges in an imagecorrespond to high frequencies in the frequency domain, while coarsetextures are represented by lower frequencies. Applied to x-ray imagesof trabecular bone, this means that a region with coarse or littletrabeculation should exhibit a Fourier spectral energy concentration atlow spatial frequencies, whereas a region of fine trabecular structureshould show a spectral energy concentration at high frequencies.

Typically, the 2-dimensional Fourier coefficients for the selected ROI.These 2-dimensional coefficients are used to determine a 1-dimensionalpower spectrum F(u) by averaging all coefficients over circles withradii that correspond to the discrete spatial frequencies u. The meantransform coefficient absolute value |F(u)| and the mean spatial firstmoment

$M_{1} = \frac{\sum\limits_{u = 2}^{N}{{{F(u)}} \cdot u}}{N - 1}$of the absolute coefficients are determined after exclusion of the first(“DC”) coefficient. M₁ provides a measure for which frequenciescontribute most to the energy of the spectrum, similar to the “center ofmass” of a geometric object.

3.1.3.4. Fractal Dimension

A different approach to analyze the texture in an image is by fractalanalysis. Fractals are objects that exhibit certain statisticalself-similar or self-affine properties, so that a portion of the object,scaled to its original size, has for example the same surface area (3-d)or the same perimeter (2-d) as the original object. In the context offractal analysis, the gray values in a particular texture can beinterpreted as an altitude, and the resulting 3-dimensional surface isanalyzed (FIG. 11).

Fractal dimension (fd) is the rate at which the perimeter or surfacearea of an object increases as the measurement scale is reduced. Russ“The Image Processing Handbook,” Third edition ed. 1999, Boca Raton: CRCpress. It is a measure for the complexity of a boundary or surface andcorresponds to the intuitive notion of an object's roughness. Withoutbeing bound by one theory, it is postulated that osteoporotic trabecularbone, in which trabeculae become thinner and lose their continuity, andtherefore complexity is increased, should have a higher fractaldimension than healthy bone.

The results from the several ways in which FD can be measured are notcomparable. Thus, various methods can be tested to determine which one(or combination) provides the best discrimination between normal andosteoporotic subjects.

The first method is applied in the frequency domain after calculation ofthe ROI's 2-D power spectrum using a fast Fourier transform (FFT). Fromthe 2-D Fourier coefficients the 1-D power spectrum is produced asdescribed above for the Fourier analysis. When this 1-D power spectrumis plotted as the logarithm of the power versus the logarithm of thefrequency, it must have a negative slope of magnitude b with 1<b<3according to fractal theory. The FD value is then calculated asFD₁=3.5−b/2.

Another approach, the Minkowski method, measures the difference (summedover the ROI) between an upper and lower envelope fitted to the surfaceas a function of the size of the neighborhood used. Peleg et al. (1984)Anal Mach Intell 6(4):518-523. If δ (δ=1, 2, 3, . . . ) is the distancebetween the envelopes and the surface, then the upper envelope u_(δ) andthe lower envelope l_(δ) are given by

u₀(i, j) = l₀(i, j) = f(i, j)${u_{\delta + 1}\left( {i,j} \right)} = {\max\begin{Bmatrix}{{{u_{\delta}\left( {i,j} \right)} + 1},\max\limits_{{{{({m,n})} - {({i,j})}}} \leq 1}} & \left\{ {u_{\delta}\left( {m,n} \right)} \right\}\end{Bmatrix}}$${l_{\delta + 1}\left( {i,j} \right)} = {\min\begin{Bmatrix}{{{l_{\delta}\left( {i,j} \right)} - 1},\min\limits_{{{{({m,n})} - {({i,j})}}} \leq 1}} & \left\{ {l_{\delta}\left( {m,n} \right)} \right\}\end{Bmatrix}}$where f(i,j) is the gray value of pixel (i,j) in the ROI. The log of thearea A(δ), plotted against log(δ), yields a line with a negative slopeof magnitude b′. The fractal dimension is then given by FD₂=2−b′. Thearea is calculated as

${A(\delta)} = \frac{v_{\delta} - v_{\delta - 1}}{2}$with

$v_{\delta} = {\sum\limits_{{({i,j})} \in {ROI}}{\left( {{u_{\delta}\left( {i,j} \right)} - {l_{\delta}\left( {i,j} \right)}} \right).}}$

3.1.3.5. Morphological Parameters

While the previous features and parameters provide rather generalinformation on trabecular bone structure, the following examplesdescribe more detailed aspects.

The gray scale region of interest is first binarized. As described inWhite et al. (1999) Oral Surg Oral Med Oral Patholo Oral Radiol Endod88:628-635, this can be achieved in the following way: The ROI isblurred by means of a Gaussian filter. The blurred ROI is thensubtracted from the original ROI, and the value 128 is added at eachpixel location. This results in an image with a mean gray value of 128,which is also used as a threshold, resulting in an image, in whichtrabeculae are white and marrow space is black.

From this binary image, the total number of white pixels represents thetrabecular area, which is calculated as a percentage of the total ROIarea. The number of pixels on the outer trabecular border measures theperipheral length of the trabeculae. The same parameters can be measuredfor the marrow space by counting the black pixels.

After skeletonization of the binary image, the total length of thetrabeculae is determined by the total number white pixels. Furthermore,counts of the terminal points and of the branch points are expressed asa proportion of trabecular length. An estimate of the average length ofthe trabeculae is calculated as the ratio of total trabecular length andthe sum of terminal points and branch points.

3.1.3.5. Markov Random Fields

In certain embodiments, Markov random fields can be used as models forosteoporosis detection from radiographic images and for fracture riskprediction. As noted herein, osteoporosis is typically manifested inradiographic images by structural changes that can be used forcomputer-aided detection and characterization. Thus, the detectionand/or characterization of osteoporosis from radiographic images relieson the measurement and analysis of a feature or set of features relatingto the density of the bone or trabecular structures present in an image.

Markov random fields can be used to analyze and detect structure densitychanges by either modeling particular joint feature distributions ({F1,F2, . . . , Fn}) as they are estimated at each image element or imageneighborhood (FIG. 19), or by modeling the actual radiographicmanifestation of particular structural definitions (e.g. trabeculae)(FIG. 20).

In the first case of estimation at each image element or imageneighborhood, the Markov random field framework is used for acontext-based feature analysis/discrimination approach which takes intoaccount local relationships between the features and effectivelycompensating for space-varying processes (e.g. variable soft tissue ormissing or incomplete data due to boundaries) that can affect therelative values of the features taken into account. (Buntine (1994)“Operations for learning with graphical models,” J. ArtificialIntelligence Res. December: 159-225).

This approach can also be used for predicting most likely fracture pathsbased on the analysis of trabecular structure nodes and their relatedfeature sets by defining the most likely chains of joint feature sets.The analysis framework can be a Likehood Ratio approach:

${\lambda = \frac{P\left( {{R\; O\; I}❘{Normal}} \right)}{P\left( {{R\; O\; I}❘{Abnormal}} \right)}},$where P(ROI|.) is given by the corresponding Markov random field model.

Another analysis approach is through the implementation and training ofBayesian networks, for example as described in Heckerman D (1996) “Atutorial on learning with Bayesian networks,” Microsoft ResearchTechnical Report, MSR-TR-95-06. based on available test case data.

Markov random fields can also be used to model the manifestations of thestructures in an image in probabilistic terms. (Geman et al. (1984)“Stochastic relaxation, Gibbs distributions, and the Bayesianrestoration of images,” IEEE Transactions on Pattern Analysis andMachine Intelligence 6:721-741; Besag (1986) “On the statisticalanalysis of dirty pictures,” Journal of the Royal Statistical Society,48(3):259-302). As depicted in FIG. 20, each of the image components(noise and characteristic structure) has associated probabilisticmodels, P(N) and P(I|T) respectively, that describe the spatialdistribution of the gray-level intensity. For example, a commonassumption for the noise component in digital/digitized radiographs isto consider Normal or Poisson distributed pixels. The nomenclature forthe distribution of the characteristic texture P(I|T) is such as toreflect that the corresponding probability distribution of the region Iis conditional (expressed by the symbol |) on the characteristicstructure present T. The analysis tools for such a probabilisticframework are provided by the laws of probability and specificallyBayes'Rule shown in FIG. 21. Bayes' rule can be described as the ruleaccording to which our knowledge about the presence of a givencharacteristic structure in an ROI is updated (a-posteriori informationrepresented by the probability distribution P(T|ROI)), based onexperience of how often (or likely) each characteristic structure ispresent (a priori information represented by the probabilitydistribution P(T)) and knowledge of how the sources of noise andvariability change the manifestation of the corresponding characteristicstructure (knowledge of the likelihood, thus also called the likelihoodfunction P(ROI|T), of the ROI image given the possible characteristicstructures and overlapping degrading components). FIG. 21 illustratesthat simply selecting the structure with the maximum a-posterioriinformation can be used as a decision criterion.

To define the likelihood function P(ROI|T), Markov random field modelingmay be employed. Markov random fields are specific multidimensionalrandom processes that satisfy what is known as the Markov property. TheMarkov property simply states that in a random series of events, eachevent can be predicted and depends only on a limited set of events. Thisproperty is convenient and intuitive for the modeling and analysis ofstructures in images. It basically states that if the distribution ofpixels in an ROI can be modeled as having the Markov property, then inorder to determine if a pixel belongs to a given structure, only alimited number of neighboring pixels are necessary.

Random fields having the Markov property confer the additional benefitof having an associated Gibbs probability distribution given by thefollowing equation:

${P\left( {{{ROI} = s_{1}},s_{2},\ldots\mspace{14mu},s_{m}} \right)} = \frac{{\mathbb{e}}^{- {U({s_{1},s_{2},\;\ldots}\mspace{14mu})}}}{z}$

Where the function:

U(s₁, s₂, …) = Σ V(s_(i)) + Σ V(s_(i), s_(j)) + Σ V(s_(i), s_(j), s_(k)) + …depends on functions V (called potentials) of local neighboring elementscalled cliques:{s_(i)},{s_(i),s_(j)},{s_(i),s_(j),s_(k)}, . . . εC

The significance of cliques is that they are the fundamental elementsthat can be used to reflect specific spatial distribution properties ofa structure of interest, such as for example vertical, horizontal anddiagonal geometries. Furthermore, the Markov property is manifested veryconveniently as each image pixel can be expressed in terms of thecliques in a local neighborhood:

${P\left( {{s_{i}❘s_{k}},{s_{k} \in N_{i}}} \right)} = \frac{{\mathbb{e}}^{- V_{N_{i}}}}{\sum\limits_{s_{c}}{\mathbb{e}}^{- {V_{N_{i}}{(s_{c})}}}}$

The model parameterization for the families of images characteristic ofa particular structural density grade and definition of a prioriinformation can be done either by estimation from available patient datathus defining empirical priors or by implementing physical andstochastic models that are based on the image generation process.

3.1.4.0. Overlapping Windows Processing

Furthermore, two or more overlapping ROIs can also be defined and usedto analyze any given image. In other words, bone density,microarchitecture, macro-anatomic and/or biomechanical (e.g. derivedusing finite element modeling) analyses can be applied within a regionof predefined size and shape and position. This region of interest mayalso be referred to as a “window.” Processing can be applied repeatedlywithin the window at different positions of the image. For example, afield of sampling points may be generated and the analysis performed atthese points (FIG. 16). The results of the analyses for each parametercan be stored in a matrix space, e.g., where their position correspondsto the position of the sampling point where the analysis occurred,thereby forming a map of the spatial distribution of the parameter (aparameter map). The sampling field can have regular intervals orirregular intervals with varying density across the image.

The amount of overlap between the windows can be determined, forexample, using the interval or density of the sampling points (andresolution of the parameter maps). Thus, the density of sampling pointsis set higher in regions where higher resolution is desired and setlower where moderate resolution is sufficient, in order to improveprocessing efficiency. The size and shape of the window would determinethe local specificity of the parameter. Window size is preferably setsuch that it encloses most of the structure being measured. Oversizedwindows are generally avoided to help ensure that local specificity isnot lost.

The shape of the window can be varied to have the same orientationand/or geometry of the local structure being measured to minimize theamount of structure clipping and to maximize local specificity. Thus,both 2D and/or 3D windows may be used, depending on the nature of theimage and data to be acquired.

In another embodiment, bone density, microarchitecture, macro-anatomicand/or biomechanical (e.g. derived using finite element modeling)analyses can be applied within a region of predefined size and shape andposition. The region is generally selected to include most or all of theanatomic region under investigation and, preferably, the parameters canbe assessed on a pixel-by-pixel basis (e.g., in the case of 2D or 3Dimages) or a voxel-by-voxel basis in the case of cross-sectional orvolumetric images (e.g., 3D images obtained using MR and/or CT).Alternatively, the analysis can be applied to clusters of pixels orvoxels wherein the size of the clusters is typically selected torepresent a compromise between spatial resolution and processing speed.Each type of analysis may yield a parameter map.

Parameter maps can be based on measurement of one or more parameters inthe image or window; however, parameter maps can also be derived usingstatistical methods. In one embodiment, such statistical comparisons caninclude comparison of data to a reference population, e.g. using az-score or a T-score. Thus, parameter maps can include a display ofz-scores or T-scores.

3.1.4.1. Analysis and Selection of Parameter Maps

The parameter maps can represent individual parameters or combinationsof parameters such as density, microarchitecture macro-anatomicalparameters or biomechanical parameters, for example derived using finiteelement modeling, are useful in identifying regions or patches that havesimilar characteristics. For instance, depending on their position,shape, size, orientation, and extent particular regions or patches thatexhibit similar characteristics (e.g., values at high or low ranges ofthe data set) typically represent regions of bone with differentproperties, for example areas of stronger or weaker areas. Therefore,parameter maps can be used to generate virtual fracture lines that aidin predicting areas of the bone that may be subject to an increased riskof fracture. One or more parameter maps can be selected by statisticalanalysis of results from in vitro mechanical loading tests or by othermeans (e.g. from cross-sectional or longitudinal studies in osteoporosissubjects, in particular those developing fractures). Selection can bebased, for example, on patch location, shape, size, orientation andextent that best correlates with location of actual fracture linesand/or for having parameter values that are best correlated withfracture risk, the incidence of osteoporotic fractures or fractureloads.

3.1.4.2. Fracture Path Prediction

When there are multiple parameter maps that correlate well with fractureline, a multivariate regression model can be fitted to generate acomposite parameter map derived from 2D or 3D data sets, e.g. x-rays,digital tomosynthesis, CT and MRI, using the techniques described hereinand/or statistical methods known to those of skill in the art. Aparameter map can be used to predict the overall bone strength orfracture risk or fracture load by analyzing the predicted fracturepaths. A predicted fracture path is defined here as the hypotheticalpath where fracture would most likely to occur, if sufficient forces areapplied in one or more particular directions.

In certain embodiments, a watershed segmentation can be applied to theselected or composite parameter map. Watershed segmentation can beapplied to 2D images as well as to 3D (cross-sectional or volumetricdata obtained, for example, from CT or MR). The boundaries of watershedsegmentation generally form along the ridges on the parameter map, i.e.,along the peak values. For a parameter that is positively correlated tobone strength or fracture load, i.e., higher values correspond tostronger bones, the inverse value of the parameter is used to generatethe watershed boundaries so that the boundaries would form along valleys(local minimum) of parameter maps. The nodes of watershed boundaries canbe identified and segmented to separate the watershed boundaries intosegments (FIG. 17). Each of these segments can be assigned a strengthvalue or fracture load value which is a composite value of one or moreparameter maps underlying the segment. The length, orientation, andposition of segments can be used as normalizing factors for the strengthvalues.

The nodes and segments of the watershed boundaries may be labeled,traced, measured, and recorded in a form of data structure, for example,a graphical structure. The strength values and interconnectrelationships are also stored for each segment. To identify the mostlikely fracture paths, a search strategy, for example, the depth-firstsearch (Russell S., Norvig, P., Artificial Intelligence: A modernapproach. 1995, NJ: Prentice Hall. pp. 77), is propagated through thedata structure to determine the paths of least resistance from onesurface of the bone to another opposite surface restricted by apredefined solid angle. Alternatively, an artificial neural network canbe trained to predict fracture paths given the parameter maps as inputs.

3.1.4.3. Fracture Risk Prediction

Having predicted one or more fracture paths, additional processing maybe performed, typically with a new processing grid that has highconcentration of nodes along the predicted fracture paths with adifferent window size and/or shape. Macro-anatomical parameters such ascortical thickness can be evaluated (in two or three dimensional images)with higher resolution at the exits of fracture paths. Parameters thatare the best predictors of fracture risk can be evaluated along thepredicted fracture paths. These parameters, including density,microarchitecture, macro-anatomical measurements and biomechanicalparameters, are selected by statistical analysis of results fromin-vitro mechanical loading test or by other means, e.g. usingcross-sectional or longitudinal studies in osteoporosis subjects, inparticular those developing fractures, for being highly correlated tothe magnitude of one or more mechanical properties of bone, for examplein one or more particular loading force directions, or for being highlycorrelated with fracture risk, incidence of new fractures or fractureloads. The mechanical properties include but are not limited to yieldingload, stiffness, and Young's modulus.

The values of parameters along the predicted fracture paths may becompared against the statistical distribution of the population. Thez-score and T-score of each parameter relates to the risk of fractureoccurring in a particular predicted fracture path. Thus, a fracture riskscore can be assigned to that fracture path. The predicted fracturepaths can also be associated with the clinical definition of commonfracture types. The overall fracture risk can then be evaluated byweighing fracture risk score of each predicted fracture path with theprobability of a particular type of fracture occurring. FIG. 18 depictsan exemplary summary of this process.

3.1.5.0. Biomechanical Assessment

The features and values extracted from the processing of density,micro-architecture, macro-anatomical parameters can be used as theinputs for biomechanical modeling, for instance modeling using finiteelement analysis. Finite element modeling (FEM) can be used as asurrogate for the physical mechanical properties of bone or composite ofbone and implants. Briefly, FEM involves the division of a structure orobject into discrete shaped elements, where the mechanical behavior ofeach element can be described by precise mathematical equations.Structural finite element analysis (FEA), a particular subset of FEM, isthe calculation of the mechanical behavior (stress and strain) at anypoint within the structure under specific loading conditions. Thefoundation of every finite element model is the two-dimensional orthree-dimensional data of the object or structure

Examples of microarchitecture and micro-anatomical features that can beused as input mesh for finite element analysis include but are notlimited to the actual and derivation of image or data structures oftrabecular structures, image or data structures of cortical bone, image,data structures of trabecular skeleton or parameter maps derived fromoverlapping window processing. As described herein, the input featurescan be obtained from 2D and/or 3D images. The application of simulatedforce can be in one or more directions, and is typically associated withthe actual force components that would occur in a fracture incident. Thefinite element analysis provides an estimate of load and direction offracture for each fracture incident scenario. Fracture risk is estimatedby weighing the fracture loads with the probability of each fracturescenario occurring. Further, the fracture paths estimated by finiteelement analysis can be used as inputs to the analysis of density,micro-architecture, macro-anatomical features. For example, density,micro-architecture, macro-anatomical features can be measured in areasof fracture paths predicted by finite element modeling. Conversely,finite element analysis can be combined with additional image andclinical data to determine fracture risk by predicting if the bone wouldfracture, given the force components that would occur in a fractureincident.

Bone fracture risk can be evaluated using one or a composite of morethan one dependent or independent results of analysis or statisticalmethods. An example of this combination is the weighted average score ofdensity, micro-architecture, macro-anatomical, finite element analysisand clinical risks factors such as weight, height, history of fracture,family history of fracture, and the like.

Finite element modeling can be applied to all of the bony structuresincluded in an image. Preferably, however, finite element modeling istypically applied in selected subregions. In certain embodiments, finiteelement modeling is applied in areas coinciding with or bordering withthe predicted fracture path, for example based on micro-structural ormacro-anatomical measurements. By combining biomechanical assessment ofbone properties with density, micro-architectural and macro-anatomicalassessment, the prediction of fracture risk and/or the correlation withfracture load can be improved. Finally, regional assessment ofbiomechanical properties can also improve the accuracy of the fracturepath prediction.

Biomechanical assessment can also include more traditional approachesestimating levers and forces at the macro-anatomical level, e.g.measurement of moments, shear and compressive forces based onmacro-geometric parameters of the bone and anticipated loads orstresses. These more traditional approaches can be combined with finiteelement modeling, measurements of density, bone structure, andmacroanatomical parameters, e.g. cortical thickness, thereby improvingassessment of bone strength and fracture risk and improving thecorrelation with fracture loads and, ultimately, incident new fractures.

As will be appreciated by those of skill in the art, the macroanatomicalparameters that are measured can change depending on the region ofinterest to be measured. For example, when studying a portion of thespine, the user can combine bone structure measurements withmacroanatomical measurements and/or FEA and/or other biomechanicalmeasurements and/or bone mineral density. The actual macroanatomicalmeasurements that are used in the spine can be, for example, the innerpedicle distance, the outer pedicle distance, the vertebral height(either anterior, central, posterior, left, right, or a combinationthereof), the vertebral anterior-posterior diameter (taken either in thesuperior, middle, inferior, or another location), the vertebral right toleft diameter (taken in either the superior, middle, inferior or anotherlocation), the vertebral diameter (taken in an oblique plane), thevertebral diagonal (using, e.g., internal cortex or external cortex),the thickness of the superior endplate (taken, e.g., anteriorly,centrally, posteriorly, from the left, from the right, or a combinationthereof), or using the thickness of the inferior endplate (again taken,e.g., anteriorly, posteriorly, from the left, from the right, or acombination thereof).

Similarly, when studying the knee and tibia, the user can combine bonestructure measurements with macroanatomical measurements and/or FEAand/or other biomechanical measurements and/or bone mineral density.However, as will be appreciated by those of skill in the art, the bonestructures used for measurements when studying the knee and tibia regionchange due to changes in anatomy. Thus, in studying the knee and tibiaregion, suitable measurements are taken from, for example, theanterior-posterior diameter of the bone using the inner or outer cortex,or a combination thereof, the medial-lateral diameter of the bone usingthe inner or outer cortex, or a combination thereof, the corticalthickness in various locations, the standard deviation of corticalthickness, the subchondral bone thickness in various locations, and/or acombination thereof.

Cases may arise where the macroanatomical measurements are used tonormalize bone structure or bone density measurements. For example, inthe tibia, bone structure and/or bone density measurements could bealtered if the patient has a tibia that is thick in theanterior-posterior dimension (e.g., thicker than average). Themacroanatomical measurements are then used to normalize the tibialmeasurement by, for example, forming a ratio between the thick tibialmeasurement in the anterior-posterior direction and another measurement.

3.2.0.0. Soft Tissue

Variations in soft tissue thickness can be significant in analyzing andevaluating bone density and bone structure, macro-anatomical parametersand biomechanical parameters, e.g. those derived using finite elementmodeling, in x-rays. Accordingly, the invention also includes methodsand devices for correcting for soft tissue in assessment of bonestructure or dense tissue, particularly for diagnosing and/or predictingosteoporosis or other bone conditions.

In certain embodiments, the x-ray image is a dental x-ray image and suchcorrection methods involve (a) interrogating at least a portion of asubject's mandible and/or maxilla with an x-ray detector; (b) producingan x-ray image of the interrogated mandible and/or maxilla; (c)obtaining data from the x-ray image regarding bone density or bonestructure; (d) interrogating the surrounding soft tissue to determinesoft tissue thickness; and (e) correcting the data obtained from thex-ray image by correcting for soft tissue thickness. Such study groupsinclude: non-osteoporotic premenopausal, non-osteoporoticpostmenopausal, osteoporotic postmenopausal patients. It will beapparent, although exemplified with respect to dental x-rays, that manyof the methods described herein can be applied to other x-ray images,e.g. hip or spine x-ray images.

Soft tissue thickness measured in a subject can also be compared toreference soft tissue thickness obtained from a control population (e.g.age-, sex-, race-, or weight-matched normal subjects). Reference softtissue thickness can be generated by measuring soft tissue thickness inhealthy subjects with normal vascular, cardiac, hepatic, or renalfunction and no other underlying medical condition. Reference softtissue thickness can be expressed as but are not limited to, mean andstandard deviation or standard error. Reference soft tissue thicknesscan be obtained independently for patients 15-20, 20-30, 30-40, 40-50,50-60, 60-70, 70-80, and 80 and more years of age and are preferablyobtained separately for men and women and for race (e.g. Asian, African,Caucasian, and Hispanic subjects). Additionally, reference soft tissuethickness can be obtained for different subject weights within each age,sex, and racial subgroup.

Individual patients can be compared to reference soft tissue thickness.If patient's soft tissue thickness is elevated, a correction factor canbe applied. The amount/magnitude of correction factor is influenced bythe magnitude of increase in soft tissue thickness that can beinfluenced by the magnitude of fat, fibrous, and muscle tissuecontribution. Clinical study groups can be evaluated to generatedatabases for further study or to generate more refined correctionfactors. Such study groups include: non-edematous non-osteoporoticpremenopausal, non-edematous non-osteoporotic postmenopausal,non-edematous osteoporotic postmenopausal; edematous non-osteoporoticpremenopausal, edematous non-osteoporotic postmenopausal, and edematousosteoporotic postmenopausal patients. In each study group the followingprocedures can be performed for comparison: dual x-ray absorptiometry(“DXA”) of the spine, hip, or calcaneus, along with SOS and BUAmeasurements or quantitative computed tomography (“QCT”). Thus,correction for soft tissue thickness can also improve the accuracy anddiscriminatory power in the analysis of x-rays and other x-rays. Suchmethods can also be used to identify population with an increased ordecreased risk of bone conditions such as osteoporosis.

4.0. Applications

The measurements of bone mineral density or trabecular architectureand/or macro-anatomical and/or biomechanical parameters, for example inthe mandible or maxilla or in the hip or in the spine, can be used toderive an assessment of bone health in any subject. Additionally, theanalysis and manipulation of data from x-rays allows for the assessmentof bone health that in turn can be used to prescribe a suitabletreatment regime. Efficacy of a treatment regime can also be assessedusing the methods and devices described herein (for example, usingmeasurements of bone mineral density or trabecular architecture and/ormacro-anatomical and/or biomechanical parameters in the mandible or themaxilla or the hip or the spine taken at two separate time points T1 andT2 to detect any difference in bone mineral density or trabeculararchitecture).

In addition, the methods described herein permit, for example, fullyautomated assessment of the structural organization and architecturalarrangement of trabecular bone and/or macro-anatomical and/orbiomechanical parameters on standard hip radiographs as well as improvedtools for monitoring progression of osteoporosis and therapeuticresponse. In certain embodiments, the methods involve binarizing andskeletonizing trabecular bone using morphological operators withdetection of branch points and endpoints of the skeleton network andclassification into free-end segments and node-to-node segments. Inother embodiments, the methods involve measuring trabecular density,trabecular perimeter, trabecular bone pattern factor, segment count,segment length, angle of segment orientation and ratio of node-to-nodesegments to free-end segments based on the binarized and/or skeletonizedimages. In still further embodiments, the methods involve (a) measuringtrabecular thickness using a Euclidean distance transform (see, alsoExample 3); (b) assessing trabecular orientation using a 2D Fast FourierTransform; and/or (c) creating a bone structure index for diagnosingosteoporosis or for predicting fracture risk combining at least two ormore of these structural parameters.

In certain embodiments, the radiograph is of a subject's hip.Furthermore, to help control the influence of radiographic positioningon the accuracy of bone structure and/or macro-anatomical and/orbiomechanical measurements, the methods may include one or more of thefollowing: evaluating the angular dependence of bone structuremeasurements in the hip, for example by comparing antero-posteriorradiographs of the hip joint in healthy to osteoporotic patients(subjects) with the femur radiographs in neutral position and in variousdegrees of internal and external rotation or by obtaining radiographs ofthe hip with different degrees of tube angulation. Bone structure and/ormacro-anatomical and/or biomechanical measurements can be comparedbetween the different positions to determine which bone structureparameters show the least dependence on radiographic positioning and/orusing a foot holder to fix the patients' foot in neutral position incase pair wise coefficients of variation between the results for the 0°neutral position and a 15° internal or external rotation position exceed10% for the majority of the structural parameters measured.

In other embodiments, methods of monitoring bone structure and/ormacro-anatomical and/or biomechanical parameters over time (e.g.,longitudinally) are also provided, for example to assess progression ofosteoporosis and/or response to therapy. In certain embodiments, themethods involve automated placement of regions of interest (ROI) in thehip joint, for example by creating and using a general model of theproximal femur that includes six defined regions of interest (ROI's).

The methods described herein, which allow, in part, for the measurementof bone structure are useful in both the diagnosis and treatment ofosteoporosis. Ultimately, these techniques could help screen largenumbers of women at risk for osteoporosis in a highly cost-effective andaccurate manner using standard, widely available radiographic equipmentwithout the need for expensive dedicated capital equipment. It is clearthat a program of this type would be powerfully enabling for therapeuticintervention with new anabolic or anti-resorptive drugs that are neededto prevent the expected pandemic of osteoporotic fractures.

4.1. Kits

The invention also provides kits for obtaining information from images,for example for obtaining information regarding bone structure,micro-architecture, macro-anatomical and/or biomechanical parametersfrom an image such as a radiograph. In certain embodiments, the kitcomprises one or more computer (e.g., software) programs, for examplefor receiving, analyzing and generating reports based on the image(s).In further embodiments, the kits can include calibration phantoms, forexample calibration phantoms integrated or attachable—to a holder,hygienic cover, x-ray film and/or x-ray film holders.

The invention also provides for therapeutic kits, for example fortreating osteoporosis or dental disease. In certain embodiments, thekits comprise a calibration phantom for use with one or more x-rayfilms, a computer software product, a database, a therapeutic drug and,optionally, instructions for use (e.g., instructions regardingpositioning the calibration phantom while taking the x-ray, using thesoftware to analyze the x-ray, dosages and the like. The therapeuticdrug can be, for example, anti-resorptive or anabolic.

4.2. Diagnosis and Prediction

In yet another aspect, methods of diagnosing or predicting bone-relateddisorders (e.g., osteoporosis, Paget's Disease, osteogenesis imperfecta,bone cancers), periodontal disease or oral implant failure in a subjectare provided, for example using any of the kits, methods and/or devicesdescribed herein. It will be apparent that these methods are applicableto any bone-related disorder including, for example, osteoporosis, bonecancer, and the like, as well as to periodontal disease and implantfailure.

Osteoporosis alone is a major public health threat for 25 millionpostmenopausal women and 7 million men. In 1995, national directexpenditures for osteoporosis and related fractures were $13 billion.Changing demographics, with the growth of the elderly population,steadily contribute to increasing numbers of osteoporotic fractures andan incipient and potentially economically unmanageable epidemic ofosteoporosis. Projections put the total cost of osteoporosis in theUnited States alone at more than 240 billion dollars per year in 40years.

Less than 20% of the patients know they have the disease and many fewerreceive physician directed specific therapy. A major impediment insuccessfully dealing with the impending osteoporosis epidemic is not alack of treatment modalities but the inability to identify persons atrisk and who require treatment. The limited access to osteoporosistesting is largely the result of the high cost of the currentlyavailable systems resulting in a small installed base limited tohospitals and specialty clinics.

The devices and methods described herein address these and other issuesby providing inexpensive and reliable bone structural analysis screensand resulting diagnosis of bone condition and/or presence of disease.Indeed, while measurements of bone mineral density (BMD) are technicallyrelatively easy to perform, low BMD accounts for considerably less than100% of fracture risk although it is well established that progressivedisruption of trabecular structure and architecture contribute in amajor way to fracture risk in older individuals.

Thus, in certain embodiments, the methods comprise using a computerprogram to analyze bone mineral density or bone structure and/ormacro-anatomical and/or biomechanical parameters of an image (e.g.,x-ray image) and comparing the value or measurement obtained from theimage with a reference standard or curve, thereby determining if thesubject has a bone-related condition such as osteoporosis or therebydetermining a subject's fracture risk. The image can also include acalibration phantom, for example a calibration phantom as describedherein.

In certain embodiments, measurements of bone structure can be combinedor correlated with measurements of macro-anatomical and/or biomechanicalparameters (e.g., cortical thickness on a hip x-ray), for example usingstatistical or mathematical methods, to create an index for the severityof the disease. Subsequently, the index can be used for diagnosingosteoporosis or for predicting fracture risk combining at least two ormore of these bone structure or morphological parameters.

4.3. Treatment

The methods and devices described herein can also be used to develop anappropriate treatment regime for a subject in need thereof.Additionally, the invention allows for the ongoing analysis of theefficacy of a subject's treatment regime.

Although estrogen deficiency after menopause is one of the most welldocumented causes of osteoporosis that can be prevented by hormonereplacement therapy (HRT), HRT may also cause an increase (approximately35%) in the risk of breast cancer in long-term users. Lancet(1997)350:1047-1059. Consequently, much effort has been devoted todeveloping alternative treatments for osteoporosis. Among thosetreatments, bisphosphonates are becoming increasingly recognized as thetreatment of choice. Lin (1996) Bone 18:75-85; Liberman et al. (1995) NEngl J Med 333:1437-1443; Mortensen et al. (1998) J Clin EndocrinolMetab 83:396-402. Another new class of therapeutic agents recentlyintroduced is the selective estrogen receptor modulators (SERMs). Delmaset al. (1997) N Engl J Med 337:1641-1647; Lufkin et al. (1998) J BoneMin Res 13:1747-1754. Anabolic therapies such as parathyroid hormonehave also been suggested for treatment of osteoporosis. Roe et al.(1999) J Bone Miner Res 14(suppl1):S137, Abst#1019; Lane et al. (1998) JClin Invest 102:1627-33.

The combined results of these and other studies suggest that effectivetreatments for osteoporosis can be developed once the condition isdiagnosed. For instance, using any of the methods, kits, and/or devicesdescribed herein, the presence of osteoporosis in a subject can bediagnosed and that subject provided with appropriate therapy (e.g., oneor more anti-resorptive agents and/or one or more anabolic agents).Periodontal disease can be similarly diagnosed and treatments rangingfrom oral hygiene practices to surgery can be recommended. Over time,the methods and compositions described herein can be used to assess theefficacy of the selected treatment and the treatment regime altered asnecessary. For example, a subject can be given a one-time or ongoingtherapy and images evaluated after such therapy to monitor itseffectiveness. Thus, in certain embodiments, treatment or monitoring oftreatment of bone related disorders are provided.

4.4. Decision Trees

Thus, diagnosing, predicting, developing treatment regimes, assessingtreatment efficacy and the like can be readily accomplished using themethods described herein. In certain aspects, these applications will beaccomplished using algorithms or decision trees (also known as logictrees or flow charts). One exemplary decision tree is provided in regardto predicting bone problems. It will be readily apparent that suchdecision trees are equally applicable to other applications (e.g.,designing treatment regimes, assessing treatment efficacy, etc.).

One exemplary method for predicting bone problems (e.g., osteoporoses,etc.), periodontal disease or oral implant failure employs a decisiontree (also called classification tree) which utilizes a hierarchicalevaluation of thresholds (see, for example, J. J. Oliver, et. al, inProceedings of the 5th Australian Joint Conference on ArtificialIntelligence, pages 361-367, A. Adams and L. Sterling, editors, WorldScientific, Singapore, 1992; D. J. Hand, et al., Pattern Recognition,31(5):641-650, 1998; J. J. Oliver and D. J. Hand, Journal ofClassification, 13:281-297, 1996; W. Buntine, Statistics and Computing,2:63-73, 1992; L. Breiman, et al., “Classification and Regression Trees”Wadsworth, Belmont, Calif., 1984; C4.5: Programs for Machine Learning,J. Ross Quinlan, The Morgan Kaufmann Series in Machine Learning, PatLangley, Series Editor, October 1992, ISBN 1-55860-238-0). Commercialsoftware for structuring and execution of decision trees is available(e.g., CART (5), Salford Systems, San Diego, Calif.; C4.5 (6), RuleQuestResearch Pty Ltd., St Ives NSW Australia) and may be used in the methodsof the present invention in view of the teachings of the presentspecification. A simple version of such a decision tree is to choose athreshold bone structure and/or macro-anatomical and/or biomechanical orbone mineral density reading at a particular anatomical landmark (e.g.,edge of mandible or maxilla, the end of a tooth root, etc.). If a valueis equal to or below the threshold bone data value, then more of theimage is evaluated. If more of the image is below the threshold value,then a bone problem, periodontal disease or implant failure ispredicted.

For example, a first level decision is made by the algorithm based onthe most recent x-ray images obtained and analyzed as described hereinis compared to initial thresholds that may indicate an impending orcurrent bone- or periodontal-related event. For example, the algorithmmay compare the current bone structure measurements (time=n) or apredicted bone structure measurement (time=n+1) to a threshold value. Ifthe bone structure measurement is greater than the threshold value thena decision is made by the algorithm to suggest further future x-rays. Ifthe bone structure measurement is less than or equal to the thresholdlevel(s) then the algorithm continues with the next level of thedecision tree.

The next level of the decision tree may be an evaluation of thesubject's age and/or gender at time (n) that x-ray is taken, which iscompared to a threshold bone measurement for “normal” subjects of thatage and/or gender. For example, if the subject's bone measurement isgreater than the threshold bone structure level for that particular ageand/or gender, then a decision is made by the algorithm to promptfurther monitoring in the future. If the information on bone structureis less than or equal to the threshold, then the algorithm continueswith the next level of the decision tree.

The next level of the decision tree may be, for example, an evaluationof the subject's soft tissue (e.g., gum) thickness (n), which iscompared to a threshold measurement. For example, if the soft tissue issignificantly below or above the normal range of thickness, then adecision is made by the algorithm to examine more of the x-ray image orto predict a bone-related problem.

The decision tree could be further elaborated by adding further levels.For example, after a determination that a bone and/or periodontal eventsare possible, the subject can be x-rayed again to see if values havechanged. Again, age, gender, weight, soft tissue thickness and the likecan also be tested and considered to confirm the prediction.

In such decision trees, the most important attribute is typically placedat the root of the decision tree. In one embodiment of the presentinvention the root attribute is the current bone structuremeasurement(s). In another embodiment, a predicted bone structuremeasurement at a future time point may be the root attribute.Alternatively, bone mineral density and/or implant structure could beused as the root attribute.

Further, thresholds need not (but can) be established a priori. Thealgorithm can learn from a database record of an individual subject'sreadings and measurements. The algorithm can train itself to establishthreshold values based on the data in the database record using, forexample, a decision tree algorithm.

Further, a decision tree may be more complicated than the simplescenario described above. For example, if soft tissue of a particularsubject is very thick, the algorithm may set a threshold for the bonemeasurements that is higher or lower than normal.

By selecting parameters (e.g., current or future bone information, etc.)and allowing the algorithm to train itself based on a database record ofthese parameters for an individual subject, the algorithm can evaluateeach parameter as independent or combined predictors of disease and/orimplant failure. Thus, the prediction model is being trained and thealgorithm determines what parameters are the most important indicators.A decision tree may be learnt in an automated way from data using analgorithm such as a recursive partitioning algorithm. The recursivepartitioning algorithm grows a tree by starting with all the trainingexamples in the root node. The root node may be “split,” for example,using a three-step process as follows. (1) The root node may be split onall the attributes available, at all the thresholds available (e.g., ina training database). To each considered split a criteria is applied(such as, GINI index, entropy of the data, or message length of thedata). (2) An attribute (A) and a threshold (T) are selected whichoptimize the criteria. This results in a decision tree with one splitnode and two leaves. (3) Each example in the training database isassociated with one of these two leaves (based on the measurements ofthe training example). Each leaf node is then recursively split usingthe three-step process. Splitting is continued until a stopping criteriais applied. An example of a stopping criteria is if a node has less than50 examples from the training database that are associated with it.

In a further embodiment, at each level of the decision in the decisiontree, the algorithm software can associate a probability with thedecision. The probabilities at each level of decision can be evaluated(e.g., summed) and the cumulative probability can be used to determinewhether disease and/or implant failure is predicted.

Receiver Operating Characteristic (ROC) curve analysis can be applied todecision tree analysis described above. ROC analysis is anotherthreshold optimization means. It provides a way to determine the optimaltrue positive fraction, while minimizing the false positive fraction. AROC analysis can be used to compare two classification schemes, anddetermine which scheme is a better overall predictor of the selectedevent (e.g., evidence of osteoporosis); for example, a ROC analysis canbe used to compare a simple threshold classifier with a decision tree.ROC software packages typically include procedures for the following:correlated, continuously distributed as well as inherently categoricalrating scale data; statistical comparison between two binormal ROCcurves; maximum likelihood estimation of binormal ROC curves from set ofcontinuous as well as categorical data; and analysis of statisticalpower for comparison of ROC curves. Commercial software for structuringand execution of ROC is available (e.g., Analyse-It for Microsoft Excel,Analyse-It Software, Ltd., Leeds LS12 5XA, England, UK; MedCalc®,MedCalc Software, Mariakerke, Belgium; AccuROC, Accumetric Corporation,Montreal, Quebec, Calif.).

Related techniques that can be applied to the above analyses include,but are not limited to, Decision Graphs, Decision Rules (also calledRules Induction), Discriminant Analysis (including Stepwise DiscriminantAnalysis), Logistic Regression, Nearest Neighbor Classification, NeuralNetworks, and Naïve Bayes Classifier.

All of these aspects of the invention can be practiced separately or incombination. Typically, the use of combinations of the embodimentslisted above is more advantageous. Further, although preferredembodiments of the subject invention have been described in some detail,it is understood that obvious variations can be made without departingfrom the spirit and the scope of the invention.

EXPERIMENTAL

Below are examples of specific embodiments for carrying out the presentinvention. The examples are offered for illustrative purposes only, andare not intended to limit the scope of the present invention in any way.

Example 1 In Vivo Reproducibility and In Vivo Diagnostic Sensitivity

A. Dental X-Rays

In order to test in vivo reproducibility of data obtained from dentalx-rays, the following experiment was performed. Subjects sat in a dentalchair and an x-ray was taken of the area of the incisor teeth and of themolar teeth of the mandible. A calibration phantom step wedge wasattached to the dental x-ray film. The dental x-ray film was exposedusing standard x-ray imaging techniques for x-rays of the incisor area.The subjects walked around for 15 minutes at which point that test wasrepeated using the same procedure.

X-ray films were digitized on a commercial flat-bed scanner withtransparency option (Acer ScanPremio ST). The regions of interest (ROIs)were placed manually at the same position with respect to the dentalroots in all digitized x-rays of the same subject using the NIH Imagesoftware program (http://rsb.info.nih.gov/nih-image/Default.html). Thereproducibility of the measurement of the average gray values inside theROIs was determined as the coefficient of variation (COV=standarddeviation of measurements/mean of measurements). Overall results aregiven as root mean square

TABLE 2 Reproducibility of measurements of average gray values indigitized dental x-rays Region COV Subject A COV Subject B RMS Incisor2.9% (n = 3) 5.9% (n = 3) 4.6% Molar 3.0% (n = 3) 4.1% (n = 4) 3.6% Allregions: 4.2%over both subjects. The data are summarized in Table 2.

$\left( {{R\; M\; S} = \sqrt{\sum\limits_{1}^{n}{x_{i}^{2}/n}}} \right)$

The data show that reproducibility is achieved that is alreadycomparable with that of many ultrasound systems to diagnoseosteoporosis.

B. Hip Radiographs

To test whether bone texture analysis in hip x-rays can detectdifferences between normal and osteoporotic bone, sample hip x-rayimages were acquired in two patients with a Fuji FCR 5000 computedradiography system (Fuji Medical Systems, Stemford, Conn.). The firstpatient had normal bone mineral density in the hip as measured by DXA.In the second patient, femoral neck BMD measured by DXA was one standarddeviation below normal.

For x-ray imaging, patients were positioned on the x-ray table in supineposition, parallel to the long axis of the table. The patient's armswere placed alongside their body. Patient comfort was ensured with apillow underneath the patient's neck. However, no pillows were usedunderneath the knees. The x-ray technologist checked that the patientlies straight on the table by looking from the head down towards thefeet (which were placed in neutral position with the toes pointing up.The ray was centered onto the hip joint medial and superior to thegreater trochanter.

Anteroposterior hip radiographs were acquired using the followingparameters: Film-focus distance: 100 cm; tube voltage: 65 kVp; exposure:phototimer for automatic exposure or approximately 20 mAs for manualexposure; collimation: limited to the hip joint, including proximalfemoral diaphysis; centering: over femoral head (see above); tubeangulation: zero degrees. An aluminum step wedge (BioQuest, Tempe,Ariz.) was included in the images to calibrate gray values beforefurther image analysis. Processing was performed using ImageJ, a Javaversion of NIH image (http://rsb.info.nih.gov/ij/).

Six regions of interest were selected manually at the approximatelocations as shown in FIG. 9. Trabeculae were extracted throughbackground subtraction. The resulting binarized images are shown in theFigures. In a next step, the trabecular bone in the selected regions ofinterest was skeletonized.

The binarized ROI's in the normal and the osteopenic patient were usedto determine the trabecular density ratio (trabecular area vs. ROIarea). The following bone structure measurements were obtained from theskeletonized ROIs; mean segment length, total skeleton length(normalized by ROI area), skeleton segment count (normalized by ROIarea), and skeleton node count (normalized by ROI area). Results areshown in Tables 3 through 7.

TABLE 3 Trabecular Density Ratio (Trabecular Area/ROI Area) ROI A ROI BROI C ROI D ROI E ROI F Normal 0.473 0.482 0.514 0.494 0.476 0.485Osteopenia 0.382 0.455 0.492 0.426 0.424 0.455 % Osteopenia 81% 94% 96%86% 89% 94% vs. Normal

TABLE 4 Mean skeleton segment length ROI A ROI B ROI C ROI D ROI E ROI FNormal 7.116 8.071 10.765 8.175 8.272 7.313 Osteopenia 7.146 9.87710.004 6.699 8.607 9.750 % Osteopenia 100% 122% 93% 82% 104% 133% vs.Normal

TABLE 5 Total Skeleton Length (normalized by ROI area) ROI A ROI B ROI CROI D ROI E ROI F Normal 0.0736 0.0758 0.0906 0.0889 0.0806 0.0785Osteopenia 0.0503 0.0589 0.0672 0.0584 0.0681 0.0543 % Osteopenia 68%78% 74% 66% 84% 69% vs. Normal

TABLE 6 Skeleton segment count (normalized by ROI area) ROI A ROI B ROIC ROI D ROI E ROI F Normal 0.0100 0.0094 0.0084 0.0109 0.0097 0.0107Osteopenia 0.0070 0.0060 0.0067 0.0087 0.0079 0.0056 % Osteopenia 68%63% 80% 80% 81% 52% vs. Normal

TABLE 7 Skeleton node count (normalized by ROI area) ROI A ROI B ROI CROI D ROI E ROI F Normal 0.0198 0.0210 0.0229 0.0244 0.0156 0.0240Osteopenia 0.0090 0.0117 0.0132 0.0113 0.0088 0.0081 % Osteopenia 46%56% 58% 47% 56% 34% vs. NormalThese results demonstrate that the evaluation of trabecular structurereveals significant differences between normal and osteopenic bone andthat selective analysis of trabeculae oriented in certain directions inthe different ROI allows for the assessment of structures critical forbiomechanical stability of the proximal femur.

C. Spine Radiographs

To test whether bone texture analysis in spine x-rays can detectdifferences between normal and osteoporotic bone, sample spine x-rayimages will be acquired in more than one patient. In the spine, the bonestructure parameters can be measured in the L1, L2, L3 and L4 vertebralbodies unless obscured by superimposed ribs, iliac crest or bowel gas.The first patient will provide control data provided the patient hasnormal bone mineral density in the spine. In the second patient andsubsequent patients, spine BMD will be measured.

Regions of interest will be selected manually at the approximatelocations as shown in FIG. 22. Trabeculae will be extracted throughbackground subtraction. In a next step, the trabecular bone in theselected regions of interest was skeletonized. FIG. 24 depicts anexample of an application of structure extraction and measurement fortherapeutic monitoring using spine x-ray. White outline of extractedstructure are show in (a) before treatment, and (b) after treatment.

D. Knee/Tibial Radiographs—Osteoporosis

To test whether bone texture analysis in knee and tibial x-rays candetect differences between normal and osteoporotic bone, sample x-rayimages will be acquired in more than one patients. The first patientwill provide control data provided the patient has normal bone mineraldensity or bone structure in the tibia or femur. In the second patientand subsequent patients, joint BMD or bone structure will be measured.

Regions of interest will be selected manually at the approximatelocations as shown in FIG. 23. The ROI can, for example, be the regionimmediately below the tibial plateau subchondral bone. Trabeculae willbe extracted through background subtraction. In a next step, thetrabecular bone in the selected regions of interest is skeletonized.

D. Knee/Tibial Radiographs—Arthritis

To test whether bone texture analysis in knee and tibial x-rays candetect differences between normal patients and patients with arthritis,sample x-ray images will be acquired in more than one patients. Thefirst patient will provide control data provided the patient has normalbone mineral density or bone structure in the tibia or femur. In thesecond patient and subsequent patients, joint BMD or structure will bemeasured.

Regions of interest will be selected manually at the approximatelocations as shown in FIG. 23. The ROI can, for example, be the regionimmediately below the tibial plateau subchondral bone. Trabeculae willbe extracted through background subtraction. In a next step, thetrabecular bone in the selected regions of interest is skeletonized.

Example 2 Image Processing Techniques

Techniques to analyze structure of trabeculae in different regions ofthe femoral head, neck, and proximal shaft are developed in Matlab (TheMathWorks, Inc., Natick, Mass.) on PC's. The following techniques(modules) are developed: algorithms for software analysis of density,length, thickness, and orientation of trabeculae in different regions ofinterest (ROI) in the radiograph and a technique for automated placementof these ROI.

Six regions of interest are selected in the proximal femur for bonemicrostructure evaluation. The size and shape of these ROI are designedto capture the local changes of trabecular density and structure (see,e.g., FIG. 9), and may reflect the location of the different compressiveand tensile groups of trabeculae. Singh et al. (1970) J Bone Joint SurgAm. 1970. 52:457-467. Thus, a classification scheme based on statisticalconvergence of multiple parameters that would provide a high precisionindex for predicting hip fractures is developed.

Example 3 Bone Structure Analysis of Hip Radiographs

The trabeculae in the femur is extracted using the backgroundsubtraction method, essentially as described in Geraets et al. (1998)Bone 22:165-173. A copy of the image is blurred with a 15×15 Gaussianfilter, and the result represents the non-uniform background. Thisbackground image is subtracted from the original image to obtain animage of trabecular structure. This image is then transformed intobinary image of trabecular structure by applying a threshold value of 0.An example of the end result is shown in FIG. 10.

In a second step, parameters relevant to the geometry and connectivityof trabecular structure are measured on the trabecular skeleton orcenterline. The skeletonization is performed using morphologicalhit-or-miss thinning for example as described in Soille, “Morphologicalimage analysis: principles and application” Springer, 1998: p. 129-154.The branch points and end points of the skeleton network are detected,and the skeleton segments are classified as free-end segments andnode-to-node segments.

One or more of the following parameters from the binarized and from theskeletonized ROI's are used: trabecular density; ratio of trabeculararea to total ROI area; trabecular perimeter; star volume (Ikuta et al.(2000) J Bone Miner Res. 18:271-277; Vesterby (1990) Bone 11:149-155);trabecular bone pattern factor (Hahn et al. (1992) Bone 13:327-330);Euclidean distance transform; assessment of trabecular orientation usingFourier analysis; and orientation-specific trabecular assessment.Further, one or more of the following parameters can be measured in eachROI on the network of skeletonized trabeculae as a whole, all skeletonsegments, and each type of segment: segment count; segment length; angleof segment orientation; and Interconnectivity Index (Legrand et al.(2000) J. Bone Miner Res. 15:13-19): normalized ratio of the number ofnode-to-node segments to free-end segments.

For example, in Euclidean Distance Transform each pixel on the binarizedtrabeculae is assigned a value equal to its Euclidean distance from thestructure boundary. Thus, thicker trabeculae will have larger distancetransform values in the center, thereby estimating trabecular thicknesscalculates the mean of the distance transform values along thetrabecular skeleton (see FIG. 11). Further, multiplying this value by 2provides a measurement of trabecular thickness.

Similarly, predominant trabeculae orientation may be evaluated using the2D Fast Fourier Transform (FFT). A rectangular region is selected withineach ROI and multiplied with a 2D Kaiser window before applying thetransform (see FIG. 12, left). The log of the Fourier magnitude is takento form an image representing the frequency domain of the ROI. Theresult is then filtered with a 5×5 Gaussian filter to reduce localvariation. An example image is shown in FIG. 12, center. The Fourierimage is subsequently thresholded at a fixed magnitude level. Thisbinary image is resampled to a square image to normalize the length ofthe vertical and horizontal axes, and the direction and length of itsmajor axis are determined (FIG. 12, right). The angles will be measuredwith respect to the axes of the femoral neck and shaft. The axes aredetermined by fitting lines to the two longest segments of thecenterline of the binarized femur (see also FIG. 14). The ROI's arelocated such that they include the different groups of compressive andtensile trabeculae in the proximal femur that each can be characterizedby a specific direction. A fully automated technique to evaluate thedifferent quantitative structural parameters explained above for thosetrabeculae in each of the ROI that are oriented in the characteristicdirection expected for the particular ROI is developed.

The orientation of each trabecular skeleton segment is found through thegradient of the line fitted to the skeleton points. Based on thisorientation information, only those trabeculae are considered in theevaluation of the structure parameters that are approximately orientedin the characteristic direction for a particular ROI.

As will be appreciated by those of skill in the art, all measurementscan be constrained by one or more desired orientation by measuring onlysegments within specified angle ranges. The statistics of watershedsegments include: number of segments, total area of segments, averagearea of segments, standard deviation of segment area, smallest segmentarea, and largest segment area. These segments are, however, general innature.

When evaluating the hip, additional parameters can be considered.Parameters include, for example, shaft angle, neck angle, diameter ofthe femur neck, the hip axis length, the largest cross-section of thefemur head, the average thickness of the cortical region within a ROI,the standard deviation of cortical thickness within a ROI, or themaximum or minimum thickness of the cortical thickness within a ROI.

In contrast, when evaluating the spine, additional parameters to beconsidered include, for example, all parameters on vertical structures,all parameters on horizontal structures, vertebral cortical thickness,maximum vertebral height, minimum vertebral height, average vertebralheight, anterior vertebral height, medial vertebral height, posteriorvertebral height, maximum inter-vertebral height, minimuminter-vertebral height, and average vertebral height.

The knee and tibial region can be evaluated using the additionalparameters of: average medial joint space width, minimum medial jointspace width, maximum medial joint space width, average lateral jointspace width, minimum lateral joint space width and maximum lateral jointspace width.

As will be appreciated by those of skill in the art, the additionalparameters listed for these exemplar anatomies above can include otherparameters. Additionally, parameters can be evaluated for otheranatomies not specifically set forth without departing from the scope ofthe invention.

Example 4 Multidimensional Classification

Example 3 describes a number of parameters that are measured to assesstrabecular structure in different regions of the proximal femur. In thisExample, the different structural parameters are combined in eachsection, and a single index is determined over all regions of interest.

A training set of hip x-ray images of a group of subjects are dividedinto the two categories “osteoporosis” and “no osteoporosis”, based onprevious DXA results. Subsequently, for all x-rays in the training set,the parameters listed in Example 3 are calculated for all regions ofinterest placed as described in Example 3, resulting in a set ofm-dimensional prototype feature vectors f_(i)=(f_(i1), . . . ,f_(im))^(T) for the training set I={I_(i)}, i=1, . . . , n.

For each parameter a single scalar index value is calculated. All indexvalues are combined into one n-dimensional feature vector. In one step,the system is trained with the data from clinical validation studieswith premenopausal, postmenopausal healthy and postmenopausalosteoporotic subjects. The subject groups are preferably divided into a“fracture” and a “no fracture” category. The feature vectors calculatedfrom the x-ray images are used as prototype patterns.

For each patient, a feature vector is calculated from the x-ray ascalculated for the prototype patterns and an individual patientclassified as category C if the majority of the k closest prototypepatterns is of the category C. The distance d between the patient'sfeature vector f=(f₁, f₂, . . . , f_(n))^(T) and a prototype patternp=(p₁, p₂, . . . , p_(n))^(T) is defined by the Euclidean norm L₂:

${d\left( {f,p} \right)} = {{L_{2}\left( {f,p} \right)} = \sqrt{\sum\limits_{i = 1}^{n}\left( {f_{i} - p_{i}} \right)^{2}}}$

The optimum scale for the different parameters is also preferablydetermined. However, for some parameters differences in the index valuesbetween the categories is smaller than for others. Also, the optimum kwill be determined. Increasing k is expected to improve the accuracy ofthe classification, but it has to be smaller than the number ofprototypes in each category. The exact percentage value of the majorityof the k closest prototype patterns that determines the classificationprovides a measure for the reliability of the classification. The higherthe percentage of prototype patterns from a particular category C, themore significant the information provided by the classification islikely to be.

This classification approach is validated with a series of leave-one-outexperiments using the 0° neutral position images of the femoral positionstudy (see Example 8) and the baseline hip x-rays of the short-term invivo reproducibility study. For these experiments, each subject ispreferably used as a test case once. The training set for the systemconsists of the patterns calculated for all or most of the remainingsubjects. The test case is correctly classified using this training set,and the diagnostic sensitivity and specificity of the combination ofbone structure parameters is determined.

In addition to the measurements described above (which provide indexvalues for the parameters “length of trabeculae”, “direction oftrabeculae and anisotropy”, and “trabecular thickness”), additionalmeasurements for other parameters in the classification system that havebeen explored in the past to study bone density and structure fromx-ray, CT, and MR images such as: (1) mean pixel intensity; (2) varianceof pixel intensity; (3) Fourier spectral analysis; (4) fractaldimension; (5) morphological parameters such as the trabecular area,trabecular periphery, total trabecular length, number of terminal andbranch points, as well as similar parameters for the bone marrow can beused.

Example 5 Automated Placement of Region of Interest (ROI)

Analysis of x-rays (e.g., hip radiographs) may be facilitated bydevelopment of techniques that locate one or more regions of interest(ROI) used for the calculation of the structural parameters of thetrabecular bone. For example, the general position of the femur can belocated using a binary image of the hip radiographs thresholded at theappropriate gray value. In a typical hip radiograph, the femur is abright structure extending from the pelvis. (FIG. 13). By thresholdingthe digitized radiograph at the typical femur intensity value, a binaryimage showing the femur is produced. The relatively thin structure ofthe femoral shaft can be extracted by applying a morphology operation onthe binary image. The morphological top-hat filter (opening subtractedfrom input) with an upright rectangular structuring element segments thefemoral shaft. The result is shown in FIG. 13 with outline of thebinarized femur superimposed on the original radiograph. The region iscropped for further processing, preferably leaving enough room toinclude the femoral head.

To position the set of predetermined ROI, a regularized active shapealgorithm can be used (Behiels et al. (1999) Proceedings of the 2ndInternational Conference on Medical Image Computing andComputer-Assisted Intervention—MICCAI'99, Lecture notes in ComputerScience 1679:128-137; Cootes (1994) Image and Vision Computing12:355-366). A general model of the proximal femur is created bymanually outlining the shape in a training set of typical hipradiographs to form a mean shape. The six predefined ROI are thenembedded into this model. This mean model is scaled down 80%,isometrically along its centerline. This transformation is applied tothe predefined ROI as well. The outline of the rescaled model is thenused as the initial template and is positioned within the proximal femurin the input image. The control points of the contour are subsequentlyexpanded outwards away from the nearest centerline point. The energyfunction to be optimized in this iterative process can take into accountlocal features, such as gradient, intensity, deviation from the meanmodel, and curvature of contour segments. FIG. 14 illustrates thepropagation of the initial control points towards the femur edge. Whenthe iteration is completed, a deformation field for the model area iscalculated. This deformation field is interpolated for the model ROIinside the boundaries of the femur model. The result is a new set of ROIthat is adapted to the input image, but similar to the model ROI withrespect to anatomical landmarks (see FIG. 9).

Example 6 Data Analysis

Patients are selected into one of three groups: healthy premenopausal(PRE); healthy postmenopausal (POST), and osteoporotic postmenopausal(OSTEO) women. All groups are studied by: (1) dental x-ray images of theperiapical and canine region; (2) quantitative computed tomography ofthe spine and (3) hip; (4) dual x-ray absorptiometry of the spine and(5) hip; (6) single x-ray absorptiometry of the calcaneus, and (7)ultrasound of the calcaneus using standard techniques. A diagnosis ofosteoporosis is made when at least one atraumatic vertebral fracture asdetermined by a semi-quantitative assessment of morphologic changes ofthe thoracic and lumbar spine on lateral conventional x-rays isobserved.

The means and standard deviations of the different bone structuremeasurements (see above) and bone mineral density measurements(mandibular BMD, QCT spine, QCT hip, DXA spine, DXA hip, SXA calcaneus,ultrasound calcaneus) are calculated for each patient group. TheStudent's t-test (t-values and p-values) and percent decrement are usedfor comparing the different measurements for reflecting intergroupdifferences. Annual, age-related changes are expressed as percentchanges relative to the predicted values at age 30 and as fractionalstandard deviation (SD) of PRE. Correlations with age along withp-values are also be reported. Odds ratios (for 1SD change in themeasured parameter) and 95% confidence limits based on the age-adjustedlogistic regression are calculated to measure the discriminative ability(for discriminating between the postmenopausal osteoporotic and thenormal postmenopausal group) and the risk of osteoporotic fractureassociated with the measured parameter. The pairwise comparisons of thediscriminative abilities are tested using age-adjusted receiveroperating characteristic (ROC) curve analysis.

Pairwise comparisons of all techniques are obtained by pooling allsubjects (PRE, POST, OSTEO) and using Pearson's correlation coefficients(r), percent standard errors of the estimate (CV), and p-values fortesting significance of correlations.

To compare measurements for their diagnostic ability, a kappa scoreanalysis is performed on the normal postmenopausal women (POST) and theosteoporotic postmenopausal women (OSTEO). This is done by classifyingevery woman from the postmenopausal groups as osteopenic if her T-scorewith respect to the reference group (PRE) is less (or in case ofstructural parameters also greater) than 2.5. The T-score for anindividual woman and a particular measurement is defined as themeasurement minus the mean measurement of young normals (PRE) divided bythe SD of the measurement in the PRE group. Note that the T-score ismeasuring the position of an individual woman with respect to the PREgroup and is different from the Student's t-value.

Example 7 Longitudinal Monitoring of Bone Structure

Algorithms and software to match follow-up dental x-rays obtained at atime point T₂ relative to baseline x-rays of the mandible obtained at anearlier time point T₁ are developed. For purposes of monitoring oftherapeutic response, bone structure parameters have to be measured atthe same location of the mandible at different points in time. Thus, inorder to compensate for differences in patient positioning and in orderto find corresponding regions of interest (ROI's) for comparison of theresults between baseline and follow-up examinations, it is desirable toregister two dental x-ray images.

Due to possible slight differences in the projection angle of the x-raybeam on the film in the two images to be registered, an elastic matchingstep is preferably included. The first step, however, is a global affinetransformation, for which the mutual information is used as a costfunction. Wells et al. (1996) Medical Image Analysis 1:35-51. The mutualinformation I_(M,N) of two images M and N is defined as

$I_{M,N} = {\sum\limits_{({m,n})}{{p_{MN}\left( {m,n} \right)}{{\log\left( \frac{p_{MN}\left( {m,n} \right)}{{p_{M}(m)}{p_{N}(n)}} \right)}.}}}$

Here, the gray values occurring in the two images are regarded as randomvariables, and the mutual information provides a measure of the strengthof the dependence between these variables. p_(M) and p_(N) are thedistributions of M and N respectively, and p_(MN) is the jointdistribution of M and N. Maintz et al. (1998) SPIE Medical Imaging—ImageProcessing. These distributions can be approximated from the marginaland joint gray value histograms, more accurately with the use of aParzen window function. Powell's method can be used as an optimizationscheme to find the best affine transformation for N to match it with M.Press et al. (“Numerical Recipes in C.” 2nd edition, 1992, CambridgeUniversity Press.

This global transformation is followed by local elastic adjustments toimprove the match. To achieve this, the conditional probabilitydensities p(n|m) are estimated from the joint histogram of the globallyregistered images. The transformation vector field t(x) is thendetermined such that N(x−t(x)) is as similar to M(x) as possible bymaximizing the local gray value correspondence, which for a fixed valueof x is defined asc _(x)(t)=∫w(x′−x)p(N(x′−t)|M(x′))dx′.

Here, w is a window function whose width determines the size of theregion that is used to compute t(x). To determine the window function,an approach similar to the one described in Warfield et al. “BrainWarping” 1999, Academic Press, p: 67-84 is used. A number ofsuccessively wider window functions w_(i) are combined into a singlewindow

${w = {\sum\limits_{i}{W_{i}w_{i}}}},$where the weights W_(i) are given as

$W_{i} = {{\frac{1}{\sum\limits_{i}{\det\left( Q_{i} \right)}}{\det\left( Q_{i} \right)}\mspace{14mu}{with}\mspace{14mu} Q_{i}} = {\int{{w_{i}\left( {x^{\prime} - x} \right)}{\nabla{N\left( x^{\prime} \right)}}{\nabla{N^{T}\left( x^{\prime} \right)}}{{\mathbb{d}x^{\prime}}.}}}}$

The exact location of the ROI after automatic placement in the baselineimage for a particular patient is kept in a database. When the patientreturns for a follow-up exam, the new image is registered with thebaseline image, and thus transformed into the coordinate system of thebaseline image. The bone structure in the registered follow-up x-ray canthen be measured at exactly the same position as in the baseline image.

Example 8 Influence of Positioning of the Femur on Bone StructuralMeasurements

The effect(s) of the positioning of the femur on each parameter of thebone structure assessments is (are) examined. Hip x-rays are obtained innormal postmenopausal women and postmenopausal women with osteoporosisin neutral position and in various degrees of internal and externalrotation.

The diagnosis of osteoporosis is made when at least one atraumaticvertebral fracture as determined by a semi-quantitative assessment ofmorphologic changes of the thoracic and lumbar spine on lateralconventional radiographs is observed. See, also, Genant et al. (1993) J.Bone Miner Res. 8:1137-1148.

Standard anteroposterior hip radiographs are obtained with the extremityat 30° internal rotation, 15° internal rotation, 0°, 15° externalrotation, and 30° external rotation. These angles are achieved byplacing the foot and ankle against a 30° or a 15° degree wedge in eitherinternal or external rotation of the femur. The foot is secured againstthe wedge using Velcro straps.

The effect of positioning is assessed by calculating the pair wisecoefficient of variation (CV %) between the results for the 0° positionand the other positions for each individual subjects. The angulardependency will be expressed for each of the angles 30° internalrotation, 15° internal rotation, 15° external rotation, and 30° externalrotation as the root-mean-square of these CV % values over all subjects.In general, parameters with the least dependency on angular positioningof the femur are selected.

If the pair wise coefficient of variation between the results for the 0°neutral position and the 15° internal or external rotation positionexceed 10% for the majority of the structural parameters measured, afoot holder that fixes the patients' foot in neutral position can beused The foot holder is designed with a base plate extending from themid to distal thigh to the heel. The base plate preferably sits on thex-ray table. The patients' foot is positioned so that the posterioraspect of the heel is located on top of the base plate. The medialaspect of the foot is placed against a medial guide connected rigidly tothe base plate at a 90° angle. A second, lateral guide attached to thebase plate at a 90° angle with a sliding mechanism will then be movedtoward the lateral aspect of the foot and will be locked in position assoon as it touches the lateral aspect of the foot. The foot will besecured to the medial and lateral guide using Velcro straps. It isexpected that the degree of involuntary internal or external rotationcan be limited to less than 5° using this approach.

Example 9 Influence of X-Ray Tube Angulation on Bone StructuralMeasurements

The effect(s) of the positioning of the x-ray tube on each parameter ofthe bone structure assessments is (are) examined. Dental x-rays areobtained in normal postmenopausal women and postmenopausal women withosteoporosis. The diagnosis of osteoporosis is made when at least oneatraumatic vertebral fracture as determined by a semi-quantitativeassessment of morphologic changes of the thoracic and lumbar spine onlateral conventional radiographs is observed. See, also, Genant et al.(1993) J. Bone Miner Res. 8:1137-1148.

Standard anteroposterior dental radiographs are obtained in the incisorregion of the mandible. The x-ray tube is aligned with an angle of 0°,10°, 20°, 30°, and −10°, −20°, and −30° relative to the dental x-rayfilm. These angles are achieved with use of a goniometer applied to themetal tube located in front of the dental x-ray tube. The dental x-rayfilm is positioned at the posterior mandibular wall in the incisorregion.

The effect of positioning is assessed by calculating the pair wisecoefficient of variation (CV %) between the results for the 0° positionand the other tube positions for each individual subject. The angulardependency will be expressed for each of the angles as theroot-mean-square of these CV % values over all subjects.

The results indicate that a 10 degree tube angulation can result in a12% error in apparent density.

A mechanical alignment system is then applied to the Rinn holder. Forthis purpose, an extension tubing is attached to the Rinn holder. Theextension tubing is designed so that its inner diameter is slightlygreater (and fits over) than the outer diameter of the dental x-raysystem metal tube (FIG. 15). The dental x-ray system metal tube is theninserted into the extension tubing attached to the Rinn holder thatreduces alignment error of the x-ray tube relative to the x-ray film.One group of patients then undergo two x-rays each of the incisorregion. The results indicate that the short-term in-vivo reproducibilityerror of dental bone density and bone structure measurements is reducedwith use of the mechanical alignment system by reducing x-ray tubeangulation relative to the dental film and the anatomic landmarks in themandible.

Example 10 Measurement of Bone Density, Bone Structure, Macro-AnatomicalParameters and Biomechanical Parameters and Selecting Therapy

An x-ray image of a mandible or a hip or spine or other bone is analyzedusing a computer program capable of assessing bone density, bonestructure, macro-anatomical parameters, or biomechanical parameters, forexample as described above. The computer program derives a measurementof one or more bone density, bone structure, macro-anatomical orbiomechanical parameters of the trabecular bone. The measurement of theparameter(s) is compared against a database containing information onsaid one or more parameters in normal, healthy age-, sex-, and racematched controls. If the patient's measurement differs by more than 2standard deviations from the age-, sex-, and race matched mean ofnormal, healthy subjects, a report is sent to the physician who thenselects a therapy based on the measurement(s).

Example 11 Measurement of Bone Density, Bone Structure, Macro-AnatomicalParameters and Biomechanical Parameters and Monitoring Therapy

One or more x-ray images (mandible, hip or spine or other bone) areobtained from a patient undergoing therapy for osteoporosis, for exampleusing an anabolic or an antiresorptive drug at two different time pointsT1 and T2. The x-rays are analyzed using a computer program capable ofassessing bone density, bone structure, macro-anatomical parameters, orbiomechanical parameters. The computer program derives a measurement ofone or more parameters of the bone for both time points T1 and T2. Themeasurement of the bone density, bone structure, macro-anatomical, orbiomechanical parameter(s) at T1 and T2 is compared against a databasecontaining information on said one or more parameters in normal, healthyage-, sex-, and race matched controls for each time point. If theresults indicate that the patient has lost 5% or more bone between timepoints T1 and T2 despite therapy, a physician selects a different, moreaggressive therapy.

Example 12 Measurement of Macro-Anatomical and/or BiomechanicalParameters

A hip radiograph is obtained using standard techniques and including acalibration phantom as described herein. The reference orientation ofhip x-rays is the average orientation of the femoral shaft.

A. Edge-Detection

A global gray level thresholding is performed using a bi-modal histogramsegmentation algorithm on the hip x-ray generates a binary imageproximal femur.

Edge-detection of the hip x-ray can be used. Optionally, edge-detectionmethods are further refined by obtaining breaking edges detected intosmall segments and characterizing the orientation of each segment,thereby obtaining the outline of proximal femur. Each edge segment isthen referenced to a map of expected proximal femur edge orientation andto a map of probability of edge location. Edge segments that do notconform to the expected orientation or are in low probability regionsare removed. Morphology operations are applied onto the edge image toconnect edge discontinuities. The edge image forms an enclosed boundaryof the proximal femur. The region within the boundary is then combinedwith the binary image from global thresholding to form the final mask ofthe proximal femur.

Within a selected region of interest, edge detection is applied.Morphology operations are applied to connect edge discontinuities.Segments are formed within enclosed edges. The area and major axislength of each segments are then measured. The regions are alsosuperimposed on the original gray level image and the average gray levelwithin each region is measured. The cortex is identified as the segmentsthat are connected to the boundary of the proximal femur mask, that hasthe greatest area, longest major axis length and has a mean gray levelabove the average gray level of all enclosed segments within theproximal femur mask. The segment identified as cortex is thenskeletonized. The orientation of the cortex skeleton is verified toconform to the orientation map of proximal femur edge. Euclidiandistance transform is applied to the binary image of the segment. Thevalues of distance transform value along the skeleton are sampled andstatistics (average, standard deviation, minimum, maximum and mod)measured.

As will be appreciated by those of skill in the art, measurements ofmacro-anatomical parameters described here can be applied to hip, spineor knee radiographs with modifications to adapt to the shape, scale andlocation of macro-anatomical features specific to the anatomical region.

1. A method to derive information regarding one or more bone parametersfrom an image comprising: (a) obtaining image data of bone from asubject; (b) defining a region of interest from the image data; (c)defining within the region of interest at least first and secondwindows, wherein the first and second windows overlap; (d) analyzinginformation in the first window to determine at least a first value fora parameter, the parameter selected from the group consisting of bonemicroarchitecture, bone macroanatomy, biomechanical parameters andcombinations thereof; (e) analyzing information in the second window todetermine at least a second value for the parameter; and (f) generatinga set of data at least in part from the first and second values.
 2. Themethod of claim 1, wherein the information in the first window isfurther analyzed to determine a third value of a second parameter;wherein the information in the second window is further analyzed todetermine a fourth value of the second parameter, and wherein the set ofdata is generated based at least in part on the first, second, third andfourth values.
 3. The method of claim 1, further comprising generating afield of sampling points of the image, the sampling points beingdistributed at regular intervals in the image, and the first windowbeing located at a first sampling point of the field of sampling points,and the second window being located at a second sampling point of thefield of sampling points.
 4. The method of claim 1, further comprisinggenerating a field of sampling points of the image, the sampling pointsbeing distributed at irregular intervals in the image, and the firstwindow being located at a first sampling point of the field of samplingpoints, and the second window being located at a second sampling pointof the field of sampling points.
 5. The method of claim 1, wherein theparameter is bone micro-architecture.
 6. The method of claim 1, whereinthe parameter is bone macro-anatomy.
 7. The method of claim 1, whereinthe image is two-dimensional.
 8. The method of claim 7, wherein image isan x-ray image.
 9. The method of claim 1, wherein the image isthree-dimensional.
 10. The method of claim 1, wherein the image is anelectronic image.
 11. The method of claim 1, wherein the subject is anosteoporosis subject.
 12. The method of claim 1, further comprisingcreating a parameter map based at least in part on the values associatedwith the parameter.
 13. The method of claim 12, further comprising: (a)generating multiple parameter maps; (b) generating a composite parametermap from the multiple parameters maps of step (a); and (c) analyzing thecomposite parameter map.
 14. The method of claim 12, further comprising:analyzing the parameter map, wherein the analysis is watershedsegmentation analysis or Markov random field analysis.
 15. The method ofclaim 12, further comprising: (a) generating a finite element model fromthe parameter map; and (b) applying simulated force vectors to thefinite element model.
 16. The method of claim 13, further comprising:(a) predicting a fracture path using the composite parameter map; and(b) evaluating one or more selected bone parameters along the predictedfracture path.
 17. The method of claim 14, further comprising: (a)predicting a fracture path using the analyzed parameter map; and (b)evaluating one or more selected bone parameters along the predictedfracture path.
 18. The method of claim 1, further comprising diagnosinga bone disease based on the generated set of data and selecting andadministering a suitable treatment to said subject based on saiddiagnosis.